Question

if the fifth term of a an ap is 1/8 and eighth term is 1/5 find the sum of 80 terms​

Answer 1

Answer:

⇒4th term=11

∴ a+3d=11

⇒8th term=2(4th term)+5

⇒a+7d=27

⇒(a+7d)−(a−3d)=27−11

⇒4d=16

⇒d=4

⇒a=−1

Formula: Sn = 2n

[2a+(n−1)d]

Sum of first 50 terms =

50/2 (2(−1)+49(4))

=25(194)=4850

4850