Dev lent Rs. 8000 to Jairam for 17 years and Rs. 4700 to Karnik for 16 years on simple interest at the same rate of interest and received Rs. 21120 in all from both of them as interest. The rate of interest per annum is:
Let rate of interest per annum = $$r\%$$
Sum lent to Jairam = Rs. 8000 for 17 years and Rs. 4700 to Karnik for 16 years
Simple interest = $$\frac{P \times R \times T}{100}$$
=> Total interest = $$(\frac{8000 \times r \times 17}{100}) + (\frac{4700 \times r \times 16}{100}) = 21120$$
=> $$1360r + 752r = 21120$$
=> $$2112r = 21120$$
=> $$r = \frac{21120}{2112} = 10\%$$
=> Ans - (B)
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