Question

a) An amount doubles in two years. What is the rate of interest per annum?​

Answer 1

Answer:

50 %

Step-by-step explanation:

SI = PRT/100

amount = amount * rate * 2 / 100

rate = 100 / 2

50 %

Answer 2

For compound interest, from rule of 72, we get the interest rate as 72/15 = 4.8%

If we work out previously, then the interest rate will be 4.73%. Below is the workout :

P * ( 1 + r )^15 = 2P where, P = Principle and r is the rate of interest in decimals

Or ( 1 + r)^15 = 2

Or, 1 + r = 2^(1/15) = 1.04729

Or, r = 1.04729 - 1 = 0.04729 I.e. 4.279% or, 4.73% Ans