Question
A sum of money amounts to Rs 8400 in 3 years and Rs 9000 in 4 years at simple interest. Find the principal and the rate of interest per annum.
Solution
Interest for the 4th year = 9000 − 8400 = Rs 600. So, simple interest per year = Rs 600. In 3 years, total interest = 3 × 600 = Rs 1800. Therefore principal = amount after 3 years − interest = 8400 − 1800 = Rs 6600. Rate of interest = (SI for 1 year / Principal) × 100 = (600 / 6600) × 100 = (60000 / 6600) = 600 / 66 = 100/11 % ≈ 9.09% Answer: Principal = Rs 6600; Rate = 9.09 % per annum.
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