Question

At what rate of simple interest a certain sum will be doubled in 15 years?
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Answer 1

Answer:

let the sum is Rs x

as the sum will be doubled

then interest will be also Rs x

rate of interest is y%

now interest is x.y.15/100

so,

x.y.15/100= x

=> y.15=100

=> y=100/15

=> y=20/3

so rate of interest is 20/3 % = 6 2/3 %