Question

At what rate of interest will a sum of money double itself in 5 years.
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Answer 1

Answer:

Considering as Simple Interest A=P(1+TR%)  

Given that, A=2P for T=5 years and R%=?

⇒2P=P(1+5R%)

2=1+5R%

5R%=1

R%=15

R%=20%

Check: Let principal be 100, A=100(1+5×20%)

A=200

If the interest is compounded.

A=P(1+R%)5

2P=P(1+R%)5

2=(1+R%)5

215=1+R%

1.1487–1=R%

R%=0.1487

R%=14.87%

Answer 2

Answer:

20%

Step-by-step explanation:

Lets take an example of 1000 rupees as the principle amount.

Therefore…

1000 x 5 x Rate / 100

= 50 x Rate = 1000

Time = 1000/50

        = 20%

To Verify

1000 x 5 x 20 / 100

= 100000/100 = 1000

Total amount = Principal value + S.I

                      = 1000+1000

                      = 2000

Hence the amount has doubled itself at the rate of 20%.