Find what is that first years in which a sum of money will become more than double in amount if put out at compound interest at the rate of 10% per annum?

Here, P(1 + 10/100)^t > 2P
⇒ (11/10)^t > 2
When t = 8 → (11/10)⁸ = 2.14358
t =7 → (11/10)⁷ = 1.9487
By trial, [11 x 11 x 11 x 11 x 11 x 11 x 11 x 11] / [10 x 10 x 10 x 10 x 10 x 10 x 10 x 10] >2
Hence, the first years in which sum of money will become more than double in amount is 8th year