Question

at what rate of simple interest will sum of money double itself in 20 years

Answer 1

the rate of simple intrest is

100/20 = 5%

Answer 2

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Here is your answer
Let the principal is P
and Rate of interest is r %
T = 20 years
A = 2p
Therefore
SI = A - P
= 2p - p
= p
As we know the formula
SI = PRT/100
$p = \frac{p \times r \times 20}{100} \\ r = \frac{p \times 100}{20 \times p} \\ r = 5\%$
Therefore Rate of interest is 5 %

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