Question

The first and last term of an A.P. are 4 and 81 respectively. If the common difference is 7. Then the sum of the A.Pis (a) 1140 (b) 440 (c) 1210 (d) 510​

Answer 1

Answer:

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Step-by-step explanation:

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Answer 2

Given,

a = 4, l = 81, d = 7

Here,

l = a + (n-1)d = 4 + (n-1)7

or, 81 = 4 + 7n - 7

or, 7n = 84

or, n = 84/7 = 12

∴ S = n/2[a+l] = 6[4+81] = 6[85] = 510.

So, your answer is (d) 510.

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