Question

sum of 5th term and 9th term of AP is 40 and the sum of the 14th term is 64 find the sum it first 20 term​

Answer 1

Answer:

240

Step-by-step explanation:

Let a be the first term and d be the common difference of the AP.

Then, A/Q

(a + 4d) + ( a + 8d) = 40

a + 6d = 20 ......(i)

and, (14/2)(2a + 13d) = 64

2a + 13d = 64/7 ........(ii)

By solving equation (i) and (ii) , we get

a = 236/7

and d = -16/7

Therefore, Sum of first 20 terms are

(20/2)(2*(236/6) + 19(-16/7))

240