Mathematics

Problem

Let the sum of an infinite G.P., whose first term is

a

and the common ratio is

r

, be 5. Let the sum of its first five terms be

\frac{98}{25}

. Then the sum of the first 21 terms of an A.P., whose first term is

10ar

n^{\text{th}}

term is

a_n

and the common difference is

10ar^2

, is equal to (a)

21 a_{11}

(b)

22 a_{11}

(c)

15 a_{16}

(d)

14 a_{16}