Question

If the sum of the first `2n` terms of the A.P. 2, 5, 8, ..., is equal to the sum of the first `n` terms of A.P. 57, 59, 61, ..., then `n` equals
A. 10
B. 12
C. 11
D. 13

Answer 1

Correct Answer - C
We have,
`(2n)/(2){2xx2+(2n-1)xx3}=(n)/(2){2xx57+(n-1)xx2}`
`rArr" "n(6n+1)=n(n+56)`
`rArr" "5n^(2)-55n=0rArrn=11" "[becausen!=0]`