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CBSE - Class 12 Mathematics Probability Worksheet
EXERCISE 13.2
Worksheet Answers
Solution:
We are provided with the probabilities of two independent events, $A$ and $B$:
The core theoretical principle governing this problem is the Multiplication Theorem for Independent Events. Two events $A$ and $B$ are defined as independent if and only if the occurrence of one does not affect the probability of the occurrence of the other. Mathematically, this is expressed as:
$P(A \cap B) = P(A) \times P(B)$ [By definition of Independent Events]
Substitute the given values into the multiplication identity:
$P(A \cap B) = \left( \frac{3}{5} \right) \times \left( \frac{1}{5} \right)$
Multiplying the numerators and the denominators separately:
$P(A \cap B) = \frac{3 \times 1}{5 \times 5}$
$P(A \cap B) = \frac{3}{25}$
The intersection $P(A \cap B)$ represents the joint probability of both events occurring simultaneously, which, for independent events, is the area of the overlapping region in the sample space defined by the product of their individual probabilities.
Final Solution: $P(A \cap B) = \frac{3}{25}$
Solution:
The problem provides two independent events $A$ and $B$ with the following probabilities:
Since $A$ and $B$ are independent events, the following axiom holds: $P(A \cap B) = P(A) \cdot P(B)$ [By the definition of independence in Probability Theory].
To find the probability of "not $B$" (denoted as $B'$ or $B^c$), we utilize the Complement Rule: $P(B') = 1 - P(B)$ [Per the Law of Complements].
$P(B') = 1 - 0.6 = 0.4$
If $A$ and $B$ are independent, then $A$ and $B'$ are also independent [Theorem: If $A$ and $B$ are independent, then $A$ and $B^c$ are independent].
Therefore, the probability of the intersection $P(A \cap B')$ is calculated as:
$P(A \cap B') = P(A) \cdot P(B')$
Substituting the given and derived values into the equation:
$P(A \cap B') = 0.3 \times 0.4$
$P(A \cap B') = 0.12$
Final Solution: $P(A \text{ and not } B) = 0.12$
Solution:
The total number of balls in the box is given by the sum of black and red balls:
$N = 10 \text{ (black)} + 8 \text{ (red)} = 18 \text{ total balls}$
Let $B$ be the event of drawing a black ball and $R$ be the event of drawing a red ball. Since the balls are drawn with replacement, the trials are independent, and the probabilities remain constant for each draw.
Probability of drawing a black ball $P(B) = \frac{10}{18} = \frac{5}{9}$
Probability of drawing a red ball $P(R) = \frac{8}{18} = \frac{4}{9}$
The event "one black and one red" can occur in two mutually exclusive ways when drawing two balls:
Since the draws are independent [By the Multiplication Rule for Independent Events, $P(A \cap B) = P(A) \cdot P(B)$]:
For Case 1 ($B$ then $R$):
$P(B \cap R) = P(B) \times P(R) = \frac{5}{9} \times \frac{4}{9} = \frac{20}{81}$
For Case 2 ($R$ then $B$):
$P(R \cap B) = P(R) \times P(B) = \frac{4}{9} \times \frac{5}{9} = \frac{20}{81}$
Because these cases are mutually exclusive [By the Addition Rule for Mutually Exclusive Events, $P(A \cup B) = P(A) + P(B)$]:
$P(\text{one black, one red}) = P(B \cap R) + P(R \cap B)$
$P(\text{one black, one red}) = \frac{20}{81} + \frac{20}{81} = \frac{40}{81}$
Final Solution: The probability that one ball is black and the other is red is $\frac{40}{81}$.
Solution:
Two events $A$ and $B$ are defined as mutually exclusive if they cannot occur simultaneously. In the language of set theory and probability, this implies that the intersection of the two events is the empty set: $A \cap B = \emptyset$. Consequently, the probability of their intersection is zero:
$P(A \cap B) = 0$ [By the definition of mutually exclusive events].
For any two events $A$ and $B$, the Addition Theorem states:
$P(A \cup B) = P(A) + P(B) - P(A \cap B)$ [Per the Axioms of Probability].
We are provided with the following values:
To isolate $p$, we subtract $\frac{1}{2}$ from both sides of the equation:
$p = \frac{3}{5} - \frac{1}{2}$
To perform the subtraction, determine the Least Common Multiple (LCM) of the denominators $5$ and $2$, which is $10$:
$p = \frac{3 \times 2}{5 \times 2} - \frac{1 \times 5}{2 \times 5}$
$p = \frac{6}{10} - \frac{5}{10}$
$p = \frac{1}{10}$
Final Solution: $p = \frac{1}{10}$
Solution:
Let $A$ be the event that person $A$ solves the problem, and $B$ be the event that person $B$ solves the problem. Based on the provided data:
Since the events are independent, the probability that both fail to solve the problem is given by the product of their individual failure probabilities [Per the Multiplication Rule for Independent Events].
The probability that the individuals fail to solve the problem is defined as the complement of the probability of success:
If the problem is to be solved, the only scenario where it is not solved is if both individuals fail independently. Let $F$ be the event that the problem remains unsolved:
$P(F) = P(A' \cap B')$
$P(F) = P(A') \times P(B')$ [Since $A$ and $B$ are independent, $A'$ and $B'$ are also independent]
$P(F) = \frac{1}{2} \times \frac{2}{3} = \frac{2}{6} = \frac{1}{3}$
The event "the problem is solved" is the complement of the event "the problem is not solved." Let $S$ be the event that the problem is solved:
$P(S) = 1 - P(F)$
$P(S) = 1 - \frac{1}{3}$
$P(S) = \frac{2}{3}$
Final Solution: The probability that the problem is solved is $\frac{2}{3}$.
Solution:
Two events $E$ and $F$ associated with the same sample space are defined as independent if and only if the probability of their intersection is equal to the product of their individual probabilities. Mathematically, the condition for independence is defined as follows:
$P(E \cap F) = P(E) \times P(F)$
[Reference: Definition of Independent Events in Probability Theory]
From the problem statement, we have the following assigned values:
To evaluate independence, we compute the product $P(E) \times P(F)$ using the values identified in Step 2:
$P(E) \times P(F) = \left( \frac{3}{5} \right) \times \left( \frac{3}{10} \right)$
Performing the multiplication of numerators and denominators:
$P(E) \times P(F) = \frac{3 \times 3}{5 \times 10} = \frac{9}{50}$
We compare the calculated product with the given value of $P(E \cap F)$:
Since $\frac{10}{50} \neq \frac{9}{50}$, it follows that $P(E \cap F) \neq P(E) \times P(F)$.
Because the condition $P(E \cap F) = P(E) \times P(F)$ is not satisfied, the events $E$ and $F$ do not meet the criteria for independence.
Final Solution: No, E and F are not independent because $P(E \cap F) \neq P(E) \times P(F)$.
Solution:
A fair coin has two outcomes: Heads ($H$) and Tails ($T$). An unbiased six-sided die has outcomes $\{1, 2, 3, 4, 5, 6\}$. The sample space $S$ for the combined experiment is the Cartesian product of these sets:
$S = \{ (H,1), (H,2), (H,3), (H,4), (H,5), (H,6), (T,1), (T,2), (T,3), (T,4), (T,5), (T,6) \}$
The total number of outcomes is $n(S) = 2 \times 6 = 12$. [By the Fundamental Counting Principle]
Event $A$: 'Head appears on the coin'
$A = \{ (H,1), (H,2), (H,3), (H,4), (H,5), (H,6) \}$
$n(A) = 6$
$P(A) = \frac{n(A)}{n(S)} = \frac{6}{12} = \frac{1}{2}$
Event $B$: '3 on the die'
$B = \{ (H,3), (T,3) \}$
$n(B) = 2$
$P(B) = \frac{n(B)}{n(S)} = \frac{2}{12} = \frac{1}{6}$
The intersection event $A \cap B$ represents the occurrence of both 'Head' and '3'.
$A \cap B = \{ (H,3) \}$
$n(A \cap B) = 1$
$P(A \cap B) = \frac{n(A \cap B)}{n(S)} = \frac{1}{12}$
Two events $A$ and $B$ are independent if and only if $P(A \cap B) = P(A) \times P(B)$. [Per the Definition of Independent Events]
Calculating the product $P(A) \times P(B)$:
$P(A) \times P(B) = \frac{1}{2} \times \frac{1}{6} = \frac{1}{12}$
Since $P(A \cap B) = \frac{1}{12}$ and $P(A) \times P(B) = \frac{1}{12}$, the condition for independence holds.
Final Solution: The events A and B are independent events.
Solution:
Let $H$ be the event that a randomly selected student reads the Hindi newspaper, and $E$ be the event that the student reads the English newspaper. Based on the provided data, we establish the probabilities:
[By Definition of Marginal and Joint Probability in Sample Space $\Omega$]
The question requires the probability that the student reads the Hindi newspaper, given that she reads the English newspaper. Mathematically, this is denoted as $P(H|E)$.
[Per the Definition of Conditional Probability: $P(A|B) = \frac{P(A \cap B)}{P(B)}$, where $P(B) > 0$]
Substituting the known values into the formula:
$P(H|E) = \frac{P(H \cap E)}{P(E)}$
$P(H|E) = \frac{0.20}{0.40}$
$P(H|E) = \frac{2}{4} = 0.5$
| Conditional Probability Component | Value |
|---|---|
| Target Event ($H \cap E$) | 0.20 |
| Given Condition ($E$) | 0.40 |
| Result ($P(H|E)$) | 0.50 |
Final Solution: The probability that the student reads the Hindi newspaper given that she reads the English newspaper is 0.5 or 50%.
Solution:
The sample space $S$ for a standard six-faced die is defined as $S = \{1, 2, 3, 4, 5, 6\}$. The total number of outcomes is $n(S) = 6$.
Event $A$ is defined as "the number is even": $A = \{2, 4, 6\}$ $n(A) = 3$ $P(A) = \frac{n(A)}{n(S)} = \frac{3}{6} = \frac{1}{2}$
Event $B$ is defined as "the number is red". Given that numbers 1, 2, and 3 are marked in red: $B = \{1, 2, 3\}$ $n(B) = 3$ $P(B) = \frac{n(B)}{n(S)} = \frac{3}{6} = \frac{1}{2}$
The intersection $A \cap B$ represents the set of outcomes that are both even and red. Looking at the sets $A = \{2, 4, 6\}$ and $B = \{1, 2, 3\}$: $A \cap B = \{2\}$ $n(A \cap B) = 1$ $P(A \cap B) = \frac{n(A \cap B)}{n(S)} = \frac{1}{6}$
Two events $A$ and $B$ are independent if and only if $P(A \cap B) = P(A) \cdot P(B)$ [Per the definition of Independent Events in Probability Theory].
Calculate the product of the individual probabilities: $P(A) \cdot P(B) = \frac{1}{2} \cdot \frac{1}{2} = \frac{1}{4}$
Compare this result with $P(A \cap B)$: $P(A \cap B) = \frac{1}{6}$ $\frac{1}{6} \neq \frac{1}{4}$
Since the product of the individual probabilities of event $A$ and event $B$ does not equal the probability of their intersection, the occurrence of one event affects the probability of the other.
Final Solution: Since $P(A \cap B) \neq P(A) \cdot P(B)$, events $A$ and $B$ are not independent.
Solution:
By the formal definition of independent events in probability theory, two events $A$ and $B$ are independent if and only if the occurrence of one does not affect the probability of the occurrence of the other. Mathematically, this is expressed as [Per the definition of Independence]:
$P(A|B) = P(A)$
$P(B|A) = P(B)$
The general formula for conditional probability is given by [Per Bayes' Theorem/Conditional Probability Axioms]:
$P(A|B) = \frac{P(A \cap B)}{P(B)}$
Since events $A$ and $B$ are independent, the intersection probability is defined as the product of their individual probabilities [Per the Multiplication Rule for Independent Events]:
$P(A \cap B) = P(A) \times P(B)$
Substituting the product rule into the conditional probability formula:
$P(A|B) = \frac{P(A) \times P(B)}{P(B)}$
Assuming $P(B) \neq 0$, we perform the algebraic cancellation:
$P(A|B) = P(A)$
Substituting the given value $P(A) = 0.3$:
$P(A|B) = 0.3$
Final Solution: $P(A|B) = 0.3$
Solution:
When a pair of fair six-sided dice is rolled, the sample space $S$ consists of all ordered pairs $(x, y)$ where $x, y \in \{1, 2, 3, 4, 5, 6\}$. The total number of outcomes is given by:
$n(S) = 6 \times 6 = 36$ [Fundamental Counting Principle]
The question requires the probability of obtaining an "even prime number" on each die. First, we identify the set of prime numbers within the set of possible outcomes $\{1, 2, 3, 4, 5, 6\}$.
Therefore, the condition "even prime number" is satisfied if and only if the outcome on a die is $2$.
Let $E_1$ be the event that the first die shows an even prime (2) and $E_2$ be the event that the second die shows an even prime (2).
Since the roll of one die is independent of the roll of the other, the joint probability is calculated as the product of the individual probabilities [Per the Multiplication Rule for Independent Events]:
$P(E_1 \cap E_2) = P(E_1) \times P(E_2)$
$P(E_1 \cap E_2) = \frac{1}{6} \times \frac{1}{6} = \frac{1}{36}$
Final Solution: The probability of obtaining an even prime number on each die is $\frac{1}{36}$.
Solution:
In a single toss of a fair six-faced die, the sample space $S = \{1, 2, 3, 4, 5, 6\}$. The total number of outcomes for one toss is $n(S) = 6$.
Let $E$ be the event of obtaining an odd number in a single toss. The odd numbers on a die are $\{1, 3, 5\}$.
Probability of getting an odd number in one toss: $P(E) = \frac{3}{6} = \frac{1}{2}$ [Per the Classical Definition of Probability].
Consequently, the probability of not getting an odd number (getting an even number) in one toss is $P(E^c) = 1 - P(E) = 1 - \frac{1}{2} = \frac{1}{2}$.
The experiment consists of tossing the die three times ($n = 3$). The tosses are independent events [Per the Multiplication Rule for Independent Events].
We are required to find the probability of getting an odd number at least once. Let $X$ be the random variable representing the number of odd numbers obtained. We seek $P(X \ge 1)$.
Using the Complement Rule: $P(X \ge 1) = 1 - P(X = 0)$, where $P(X = 0)$ is the probability of getting no odd numbers in all three tosses.
For $X = 0$, the outcome of every toss must be an even number. Since the tosses are independent, the joint probability is the product of individual probabilities:
$P(X = 0) = P(\text{Even}_1) \times P(\text{Even}_2) \times P(\text{Even}_3)$
$P(X = 0) = \left(\frac{1}{2}\right) \times \left(\frac{1}{2}\right) \times \left(\frac{1}{2}\right) = \left(\frac{1}{2}\right)^3$
$P(X = 0) = \frac{1}{8}$
Applying the Complement Rule to find the probability of at least one success:
$P(\text{At least one odd}) = 1 - \frac{1}{8}$
$P(\text{At least one odd}) = \frac{8 - 1}{8} = \frac{7}{8}$
Final Solution: The probability of getting an odd number at least once in three tosses is $\frac{7}{8}$.
Solution:
Let $H$ be the event that a student reads the Hindi newspaper, and $E$ be the event that a student reads the English newspaper. Based on the provided data, the probabilities are defined as follows:
To find the probability that a student reads at least one of the two newspapers, we employ the Addition Theorem of Probability [Per the Addition Rule for Sets]:
$P(H \cup E) = P(H) + P(E) - P(H \cap E)$
Substituting the given values:
$P(H \cup E) = 0.6 + 0.4 - 0.2$
$P(H \cup E) = 1.0 - 0.2 = 0.8$
The event "reads neither Hindi nor English newspapers" is represented by the complement of the union, denoted as $P((H \cup E)')$. [By De Morgan's Law and Complementary Probability Axiom]:
$P((H \cup E)') = 1 - P(H \cup E)$
$P((H \cup E)') = 1 - 0.8$
$P((H \cup E)') = 0.2$
| Event | Probability |
|---|---|
| Hindi only | $0.6 - 0.2 = 0.4$ |
| English only | $0.4 - 0.2 = 0.2$ |
| Both | $0.2$ |
| Neither | $1 - (0.4 + 0.2 + 0.2) = 0.2$ |
Final Solution: The probability that a student reads neither Hindi nor English newspapers is 0.2 (or 20%).
Solution:
We are given two independent events, $A$ and $B$, with the following probabilities:
Since $A$ and $B$ are independent events, the occurrence of one does not affect the probability of the occurrence of the other. Consequently, their complements $A^c$ and $B^c$ are also independent [By the Law of Independent Complements].
The probability of the complement of an event is defined as $P(E^c) = 1 - P(E)$. Therefore:
The event "neither $A$ nor $B$" is represented set-theoretically as the intersection of the complements of $A$ and $B$: $A^c \cap B^c$.
Per De Morgan's Law, $A^c \cap B^c = (A \cup B)^c$. Given the independence of the events, the probability of the intersection is the product of the individual probabilities [By the Multiplication Rule for Independent Events]:
$P(A^c \cap B^c) = P(A^c) \times P(B^c)$
Substituting the values derived in Step 2:
$P(\text{neither } A \text{ nor } B) = 0.7 \times 0.4$
$P(\text{neither } A \text{ nor } B) = 0.28$
Final Solution: $P(\text{neither } A \text{ nor } B) = 0.28$
Solution:
Let $H$ be the event that the student reads the Hindi newspaper, and $E$ be the event that the student reads the English newspaper. Based on the provided data, we assign the following probabilities:
We are required to find the probability that a student reads the English newspaper given that she already reads the Hindi newspaper. Mathematically, this is expressed as the conditional probability $P(E|H)$.
According to the Definition of Conditional Probability, for any two events $A$ and $B$ where $P(B) > 0$:
$P(A|B) = \frac{P(A \cap B)}{P(B)}$
[By the axioms of conditional probability theory]
Substituting the values defined in Step 1 into the formula:
$P(E|H) = \frac{P(E \cap H)}{P(H)}$
$P(E|H) = \frac{0.20}{0.60}$
Simplifying the fraction:
$P(E|H) = \frac{2}{6} = \frac{1}{3}$
| Event | Probability |
|---|---|
| Reads Hindi ($H$) | 0.60 |
| Reads English ($E$) | 0.40 |
| Reads Both ($H \cap E$) | 0.20 |
Final Solution: The probability that the student reads the English newspaper given that she reads the Hindi newspaper is $\frac{1}{3}$ (or approximately 0.333).
Solution:
We are provided with the probabilities of two independent events, $A$ and $B$:
The events are stated to be independent, which implies that the occurrence of one does not affect the probability of the other [Definition of Independent Events].
To find $P(A \text{ or } B)$, we must calculate the union of the two events, denoted as $P(A \cup B)$. The Addition Theorem of Probability states:
$P(A \cup B) = P(A) + P(B) - P(A \cap B)$
Since $A$ and $B$ are independent events, the probability of both occurring simultaneously is the product of their individual probabilities [Multiplication Rule for Independent Events]:
$P(A \cap B) = P(A) \times P(B)$
$P(A \cap B) = 0.3 \times 0.6$
$P(A \cap B) = 0.18$
Substitute the known values into the expression derived in Step 2:
$P(A \cup B) = 0.3 + 0.6 - 0.18$
$P(A \cup B) = 0.9 - 0.18$
$P(A \cup B) = 0.72$
Final Solution: $P(A \text{ or } B) = 0.72$
Solution:
The sample space $S$ consists of a well-shuffled standard deck of cards. The total number of outcomes is $|S| = 52$.
Using the classical definition of probability $P(A) = \frac{|A|}{|S|}$:
$P(E) = \frac{|E|}{|S|} = \frac{13}{52} = \frac{1}{4}$ [By the classical probability axiom]
$P(F) = \frac{|F|}{|S|} = \frac{4}{52} = \frac{1}{13}$ [By the classical probability axiom]
The intersection event $E \cap F$ represents the event that the card drawn is both a spade and an ace. There is exactly one card in the deck that satisfies both conditions: the Ace of Spades.
$|E \cap F| = 1$
$P(E \cap F) = \frac{|E \cap F|}{|S|} = \frac{1}{52}$
Two events $E$ and $F$ are independent if and only if $P(E \cap F) = P(E) \cdot P(F)$ [By the definition of independent events].
Calculate the product of individual probabilities:
$P(E) \cdot P(F) = \left(\frac{1}{4}\right) \cdot \left(\frac{1}{13}\right) = \frac{1}{52}$
Compare with $P(E \cap F)$:
Since $P(E \cap F) = \frac{1}{52}$ and $P(E) \cdot P(F) = \frac{1}{52}$, the condition $P(E \cap F) = P(E) \cdot P(F)$ is satisfied.
Final Solution: Since $P(E \cap F) = P(E) \cdot P(F) = \frac{1}{52}$, the events E and F are independent.
Solution:
According to the axiomatic definition of probability, two events $A$ and $B$ are defined as independent events if and only if the occurrence of one does not affect the probability of the occurrence of the other. Mathematically, this condition is expressed via the Multiplication Rule for independent events:
$P(A \cap B) = P(A) \times P(B)$
[By the Definition of Stochastic Independence in Probability Theory]The problem provides the following numerical values for the events $A$ and $B$:
To determine the intersection probability $P(A \cap B)$, we substitute the given values into the derived formula from Step 1:
$P(A \cap B) = 0.3 \times 0.4$
$P(A \cap B) = 0.12$
| Variable | Probability |
|---|---|
| $P(A)$ | $0.3$ |
| $P(B)$ | $0.4$ |
| $P(A \cap B)$ | $0.12$ |
Final Solution: $P(A \cap B) = 0.12$
Solution:
For any two events $A$ and $B$, the events are defined as independent if and only if the probability of both events occurring simultaneously is the product of their individual probabilities. This is expressed by the Multiplication Rule for independent events:
$P(A \cap B) = P(A) \times P(B)$
[Justification: By the definition of independent events in probability theory, the occurrence of $A$ does not affect the probability of $B$, and vice versa.]
From the problem statement, we are provided with the following initial parameters:
Substitute the given values into the formula derived in Step 1:
$P(A \cap B) = 0.3 \times 0.6$
$P(A \cap B) = 0.18$
In the diagram above, the overlapping region represents the intersection $P(A \cap B)$, which contains the probability of both events occurring simultaneously.
Final Solution: The probability of both events A and B occurring, $P(A \cap B)$, is $0.18$.
Solution:
The problem provides the probabilities of two independent events, $A$ and $B$:
Since events $A$ and $B$ are independent, the probability of their intersection is defined as [Per the definition of independent events]:
$P(A \cap B) = P(A) \times P(B)$
Substituting the given values into the multiplication rule for independent events:
$P(A \cap B) = 0.3 \times 0.4$
$P(A \cap B) = 0.12$
To find the union of two events $P(A \cup B)$, we utilize the General Addition Theorem of Probability [Per the Addition Law of Probability]:
$P(A \cup B) = P(A) + P(B) - P(A \cap B)$
Insert the known values into the addition theorem formula:
$P(A \cup B) = 0.3 + 0.4 - 0.12$
$P(A \cup B) = 0.7 - 0.12$
$P(A \cup B) = 0.58$
Final Solution: $P(A \cup B) = 0.58$