Question

What is the least number of complete years in which a sum of money put out at 20% compound interest will be more than double?​

Answer 1

Answer:

Let the numbers of years be n

Amount (A) after n years = P (1 + 20/100)n

According to the question

Amount (A) after n years > 2*Principle

P(1 + 20/100)n > 2P

(1 + 20/100)n > 2

(6/5)n > 2

Let n = 4

Then ,

(6/5)4 = 2.0736

Hence (6/5)4 > 2

So, at least 4 years is required to get an amount that id double of the original principle

Answer 2

Let Principal amount =RsP

formula of compound interest,

Amount =P(1+r/m)^mt

Acc. to question, 

2P=P(1+10/200)^t

⇒2=(1.2)^t

⇒t=4 

Hope it helps!

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