Discussion of Question with ID = 008 under Compound-Interest

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An amount P is invested for 2 years @7% p.a. The simple interest is Rs. 6000. What would be the compound interest on the same amount, at the same rate and for the same time, compounded annually?


Rs. 6210.


Rs. 6310.


Rs. 6110.


Rs. 6410.

Ans: a

Let SI, P, r, t have usual meanings. Then, for 2 years, SI = (P × r × 2)/100. So P = $(50 × SI)/r$. The compound interest for 2 years by shortcut formula is ${P × r × (200 + r)}/10000$. Putting P here, it becomes, ${{(50 × SI)/r} × r × (200 + r)}/10000$ = ${SI × (r + 200)}/200$ = ${6000 × (7 + 200)}/200$ = Rs. 6210.

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