How many terms of 1,4,7........are needed to make the sum of 715

A. 21

B. 22

C. 23

D. 24

Answer: Option B

Solution(By Examveda Team)

s=n/2{2a+(n-1)d}
715=n/2{2X1+(n-1)3}
1430=n(2+3n-3)
3n^2-n-1430=0
3n^2-(66-65)n-1430=0
3n(n-22)-65(n-22)=0
(n-22)(3n-65)=0
=>n-22=0
n=2