Question

a sum of money placed at compound interest doubles itself in 5 years.it will amount to 8 times itself at the same rate of interst

Answer 1

different between your measure

Answer 2

Answer:

15 years.

Step-by-step explanation:

Let's assume  'x' amount of money was placed initially.

Thus according to the question,  after 5 years it'll double, making it 2x.

Now 2x will act as the balance here.

Thus after 5 years it'll be doubled, that means = 2 X (2x) = 4x

So after 10 years now the amount is 4x.

Again after 5 years it'll double and reach the amount 8x,

which is 8 times the initial amount(x).

Thus the time needed for the money to become 8 times is 15 years.

Another approach is,

8 = 2ⁿ

where, n = 3

Thus time needed = 5 X 3 = 15 years.