NDA 2017 Maths · Mathematics · Sequences and Series · medium

Three geometric means are inserted between 3 and 48. Their sum is

Single correct option

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Answer: (B) $42$

Five terms in GP:

3r^4=48\Rightarrow r=2

(taking the positive ratio). The means are

6,12,24

, with sum 42. Using

r=\pm2

and picking the negative ratio would give a different sum, so the positive real GP is the standard reading.

Original question written in the NDA 2017 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake