UPSC CDS Math Simple and Compound Interest Questions

Let the principal, rate of interest and time at which sum will become6 times be ₹ P, r% p.a. and n years,respectively.⇒r=

2×100

5

=40
Now,6P=P+

P×40×n

100

⇒n=

5×100

40

=12.5 years
Trick :
Suppose you have deposited ₹100 in bank. Then in five years, it will become ₹300 and in the next 5 years, it will become ₹500 and in the next 2.5 years, it will become ₹600, which is 6 times of principal. So, total time