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### Question

The compound interest on a certain sum of money at 3% for a period of 2 years is Rs. 5481. What is the SI on this sum if the rate is halved, and time doubled?

**A**

Rs. 5400.

**B**

Rs. 5500.

**C**

Rs. 5300.

**D**

Rs. 5600.

**Soln.**

**Ans: a**

The shortcut formula is CI = Pr(r + 200)/10000. Putting CI = 5481, r = 3, we get 5481 = ${P × 3 × (3 + 200)}/10000$. We can solve it to get P = Rs. 90000. The SI = P × (2 × t) × (r / 200) = P × t × (r / 100). Putting t = 2, r = 3 and P = 90000, we get SI = Rs. 5400.