At what rate percent compound interest per annum will be rupees 6 40 amount to rupees 774.40 in 2 years?

At what rate percent compound interest per annum will Rs 640 amount to Rs 774.40 in 2 years?

Let the rate of interest be R % .Then, \[A = P \left( 1 + \frac{R}{100} \right)^n \]\[774 . 40 = 640 \left( 1 + \frac{R}{100} \right)^2 \]\[ \left( 1 + \frac{R}{100} \right)^2 = \frac{774 . 40}{640}\]\[ \left( 1 + \frac{R}{100} \right)^2 = 1 . 21\]\[ \left( 1 + \frac{R}{100} \right)^2 = \left( 1 . 1 \right)^2 \]\[\left( 1 + \frac{R}{100} \right) = 1 . 1\]\[\frac{R}{100} = 0 . 1\]R = 10

Thus, the required rate of interest is 10 % per annum.

Concept: Rate Compounded Annually Or Half Yearly (Semi Annually)

  Is there an error in this question or solution?