Question

If some amount of money is borrowed at simple interest, then 720 rupees for two years and then 1020 rupees for another 5 years, if it is principal + interest respectively, what is the percentage of annual interest rate?​

Answer 1

Principal + SI for 2 years = 720 Rs. ……(I)

Principal + SI for 7 years = 1020 Rs. ……(II)

Subtracting equation (I) from (II),

S.I. for 5 years = (1020 – 720) = 300 Rs.

∴ S.I. for 2 years = $300\times \frac{2}{5}$ = 120 Rs.

∴ Principal = (720 – 120) = 600 Rs.