Discussion of Question with ID = 074 under Compound-Interest

This is the discussion forum for this question. If you find any mistakes in the solution, or if you have a better solution, then this is the right place to discuss. A healthy discussion helps all of us, so you are requested to be polite and soft, even if you disagree with the views of others. The question and its current solution has also been given on this page.

Question

An interest rate of 4% compounded half-annually is offered by a bank. An account holder deposits Rs. 10000 in the bank under this scheme. After six months he again deposits Rs 10000. What is the total amount that he will get after 1 year?

A

Rs. 20604.

B

Rs. 21316.

C

Rs. 21116.

D

Rs. 21416.

Soln.
Ans: a

Let P, A, r and n have their usual meanings. For the first deposit n = 2, and for the second deposit n = 1. So total amount is P × \$((1 + r/100)^2 + (1 + r/100))\$ = \$P/10000\$ × \$((100 + r)^2 + 100(100 + r))\$ = \$P/10000 × (100 + r)\$ × \$(100 + r + 100)\$ which equals \${P × (100 + r) × (200 + r)}/10000.\$ Putting r = 2 and P = 10000 and cancelling 10000, we get 1 × 102 × 202 = Rs. 20604. Please note that the rate of interest will be 1/2 because the compounding is half yearly.