Question

If the first term of a G.P. be 5 and common ratio be $- 5$, then which term is 3125.

• A.
• B.
• C. $7 ^ { t h }$
• D.

Answer 1

Answer: (B)

Answer 2

Given that first term $a = 5$ and common ratio $r = - 5$

Suppose that $n ^ { t h }$term is 3125,

Then $a r ^ { n - 1 } = 3125 \Rightarrow 5 ( - 5 ) ^ { n - 1 } = 3125 \Rightarrow ( - 5 ) ^ { n - 1 } = 5 ^ { 4 }$

Hence $n = 5$.