RRB NTPC Prelims Model Paper 3 with solutions

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Question : 100 of 100

Marks: +1, -0

A sum of money doubles itself in 7 years. In how many years does it become four fold at the same rate of simple interest ?

21 years
28 years
35 years
14 years

Solution:

(1)

t_2=[n_2-1/n_1-1]^t

Here,

n_1=2;n_2=4

t=71

∴t_2=[{4-1}/{2-1}]^7

t_2={3×7}/1

t_2=21 years

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