Question

A sum of money placed at compound interest doubles itself in 3 years in how many years will it amount to 8 times itself

Answer 1

Answer:

9 years

Hope this helps.

Step-by-step explanation:

Let P be the starting principal.

After 3 years, the amount is

2P.

As it is compounding interest, we keep multiplying by the same factor for each equal time period  (unlike simple interest where we add the same amount for each equal time period).

So, after another 3 years it doubles again to give

2 × 2P = 4P

and after yet another 3 years, it doubles again to give

2 × 4P = 8P.

So it is 8 times the starting amount after a total of 9 years.