15. At what rate per cent of interest will a sum of money become 6 times itself in
15 years?​

The rate of interest will be 40%

Step-by-step explanation:

So first consider the principal to be x

Then the SI (Simple interest) will become six times of itself that is 6x

The time is 15 years

Rate = SI × 100 / P × T

Now put the values

Rate = 6 × x × 100 / x × 15

Then after simplifying the rate will come 40 %

step-by-step explanation: