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Answered on 30/11/2016 Tuition/Class IX-X Tuition Tuition/Class IX-X Tuition/Mathematics Progressions

Find the number of terms of the A.P: 7, 13, 19, ...., 205?

Tapas Bhattacharya

Tutor

The first term, t1=a = 7. The common difference, b=13 - 7=6. Last term or the nth term, tn=a + (n-1)b = 205. So, we have, 7 + (n - 1)6 = 205 --> (n - 1) = (205 - 7)/6 = 33 --> n = 34. Answer: Number of terms is 34.

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Answers 6 Comments Answered on 01/12/2016 Tuition/Class IX-X Tuition Tuition/Class IX-X Tuition/Mathematics Progressions

For the given A.P write the first term and the common difference: 3, 1, -1, -3, ..?

Tapas Bhattacharya

Tutor

The first term is 3. The common difference = 1-3 = -2.

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Answers 1 Comments Answered on 01/12/2016 Tuition/Class IX-X Tuition Tuition/Class IX-X Tuition/Mathematics Progressions

Write the first four terms of the A.p, when the first term a and the common difference d are given: a = 10, d = 10?

Tapas Bhattacharya

Tutor

The first four terms are 10, 10 + 10, 10 + 2x10, and 10 + 3x10. So, the terms are: 10, 20, 30, 40.

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Answers 1 Comments Answered on 01/12/2016 Tuition/Class IX-X Tuition Tuition/Class IX-X Tuition/Mathematics Progressions

The sum of the first six terms of an A.p is zero and the fourth term is 2. Find the sum of its first 30 terms?

Tapas Bhattacharya

Tutor

Let the first term be (a - 5b) and the common difference be 2b. So the six terms are: (a - 5b), (a - 3b), (a - b), (a + b), (a + 3b), (a + 5b). By the given conditions:- Sum of six terms=(a - 5b) + (a - 3b) + (a - b) + (a + b) + (a + 3b) + (a + 5b) = 6a=0. So, a=0. The fourth term=a + b=2 --> 0 + b=2 --> b = 2. So, for the A.P. the first term x = (a - 5b) = -10. The common difference, y = 2b = 4. Sum of 1st 30 terms, S30 = (n/2)[2x + (n-1)y] = 15 x [ -20 + 29 x 4] = 1440. (Answer)

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Answers 1 Comments Three numbers are in A.P. If the sum of these numbers be 27 and the product 648, find the numbers?

Tapas Bhattacharya

Tutor

Let the 3 terms are (a - b), a, and (a + b). So, (a - b) + a + ( a + b) = 27=> 3a=27 => a=9. Now the product is 648. So, (9 - b) x 9 x (9 + b) = 648=> (81 - b^2) = 648/9 = 72=> b^2 = 81 - 72=9 => b = =3 or b = -3. For, b = 3, the numbers are: (9 - 3), 9, (9 + 3) = 6, 9, 12 or (9 - (-3)), 9 , (9 + (-3)) = 12, 9, 6 The three numbers are 6, 9, 12 or 12, 9, 6 (Answer)

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Answers 1 Comments An A.P consists of 60 terms. If the first and the last terms be 7 and 125 respectively, find 32nd term?

Tapas Bhattacharya

Tutor

Let the first term be a and the common difference be b. So, t1 = a = 7 and t60 = a + 59b = 125. From above, we get:- t60 - t1 = 59b = 125 - 7 = 118. So, b = 118/59 = 2. Hence, the 32nd term, t32 = a + 31b = =7 + 31x2 = 69. (Answer)

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Answers 1 Comments In a certain A.P the 24th term is twice the 10th term. Prove that the 72nd term is twice the 34th term?

Tapas Bhattacharya

Tutor

Let the first term be a and the common difference be b. So, by the given condition:- t24=2 x t10 --> a + 23 b = 2 ( a + 9b) = 2a + 18b. This gives: a = 5b. So, the 72nd term: t72 = a +71b = 5b + 71b = 76b. and the 34th term: t34 = a + 33b = 5b + 33b = 38b = 76b/2 = t72/2. So, the 72nd term is twice the 34th term. (Proved)

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Answers 1 Comments Find the A.P whose 10th term is 5 and 18th term is 77?

Tapas Bhattacharya

Tutor

Let the first term be a and the common difference be b. So, the 10th term: t10 = a + 9b = 5. and, the 18th term: t18 = a + 17b = 77. So, from t17 - t10 we get: 8b = 77 - 5 = 72. This gives: b = 9. From t10 we get: a = 5 - 9b = 5 - 9x9 = -76. So, a = -76, b = 9 and the A.P is:- -76, -67, -58, -49, ..... (Answer).

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Answers 1 Comments If the 3rd and the 9th terms of an A.P are 4 and -8 respectively, which term of this A.P is zero?

Tapas Bhattacharya

Tutor

Let the first term and the common difference are a and b. So, the third term: t3=a + 2b=4. and, the 9th term: t9=a + 8b=-8. So, t9 - t6=6b = -8 - 4=-12 --> b=- 2. So, from the expression of t3, we get: a=4 - 2b=4 + 4=8. Let us consider that the nth term is zero. So: tn=a + (n-1)b = 0 --> 8 + (n-1)(-2) = 0 --> 8 -2n +2 = 0 --> 2n=10 --> n = 5. Answer: The 5th term of the series is zero.

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Answers 1 Comments Answered on 23/11/2016 Tuition/Class IX-X Tuition Tuition/Class IX-X Tuition/Mathematics Progressions

The 17th term of an A.P exceeds its 10th term by 7. Find the common difference?

Sarvajeet Kumar

Tutor

1.

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