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Find the sum of first 40 terms of the arithmetic progression whose 7th term is 21 and the common difference is 3.

Find the sum of first 40 terms of the arithmetic progression whose 7th term is 21 and the common difference is 3. Correct Answer 2460

Given:

7th term is 21 and common difference is 3

Formula used:

In an arithmetic progression, nth term = a + (n – 1) d, where a = first term and d = common difference

Sum of first n terms = n/2 ×

Calculation:

d = 3

7th term = a + 6d = 21

⇒ a + 6 × 3 = 21

⇒ a = 3

So, the first term of the series = 3

Sum of first 40 terms = 40/2 ×

⇒ 20 ×

⇒ 20 × 123 = 2460

∴ the sum of first 40 terms of arithmetic progression = 2460

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