Question

In how many years will a sum of money double itself at 10% interest per annum?

Answer 1

sum of money double itself means, interest is equals to sum
i.e. Amount = sum + SI = 2×sum
∵ SI = (P×R×T)/100
⇒P = (P×10×T)/100
⇒T = 10 years

Answer 2

please see the attachment.