Question

at rate of simple intrest wiil a sum of money double iteself in 20years

Answer 1

HEYA MATE, HERE IS UR ANSWER ____________________________

Let the principle be x.
Then Sum=2x.
Time =20 years
Rate =?

We know that

sum =PRT/100
2x=x×R×20/100
2x=xR/5
By cross multiplication
5×2x=xR
10x=xR

10=R

So rate of interest =10%

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Answer 2

Let the principal be RS 100

∴ amount = 2× 100= RS 200   [sum of money double iteself]

∴SI= RS 100     [SI =A-P]  ⇒  [RS 200 -RS 100]

Time 20 years

SI= {P*T*R] ÷100 ⇒R = {SI×100} ÷[P×T]

R = {100×100} ÷[100×20]

R = {10000} ÷[2000]

R = 5 Years       ANS