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### Question

The compound interest on a certain sum of money at 6% for a period of 2 years is Rs. 8652. What is the SI on this sum if the rate is halved, and time doubled?

**A**

Rs. 8400.

**B**

Rs. 8500.

**C**

Rs. 8300.

**D**

Rs. 8600.

**Soln.**

**Ans: a**

The shortcut formula is CI = Pr(r + 200)/10000. Putting CI = 8652, r = 6, we get 8652 = ${P × 6 × (6 + 200)}/10000$. We can solve it to get P = Rs. 70000. The SI = P × (2 × t) × (r / 200) = P × t × (r / 100). Putting t = 2, r = 6 and P = 70000, we get SI = Rs. 8400.