Question

if the first term of an AP is 3, the sum of the first five terms are 1/11 of the sum of the next five terms. Find the 20th term

Answer 1

A=3

S(10terms ) - S(5terms ) = 1/11 of S (5to 10terms ) ......(a)


Use S(“n” terms ) = n/2 * [2a +(n-1) d ]


Then after putting values given in equation ( a) u get

15 + 10d = 15/11 + 35d/11

Solve this.
U will get

165 +110d = 15 + 35d
150= -75d
D=-2

So now a(20) = a+19d
= 3 + 19(-2)
=-35