Question

A sum of Rs. 1,780 become Rs. 2,136 in 4 years, Find:
(i) the rate of interest.
(ii) the sum that will become Rs. 810 in 7 years at the same rate of interest?

Answer 1

(i) In the first case, Principal (P) = Rs. 1780

Amount (A) = Rs. 2136

∴ S.I. = A - P = Rs. 2136 - 1780 = Rs. 356

Time (T) = 4 years

∴ Rate = `("S.I." xx 100)/("P" xx "T")`

`= (356 xx 100)/(1780 xx 4) = 5 % "p.a"`

(ii) In second case, Let principal (P) = Rs. 100

Rate (R) = 5% p.a., Time (T) = 7 years

∴ S.I. = `("P" xx "R" xx "T")/100`

`= (100 xx 5 xx 7)/100` = Rs. 35

∴ Amount = P + S.I. = Rs. 100 + 35 = Rs. 135

If the amount is Rs. 135, then the principal = Rs. 100 and if the amount is Rs. 810, then the principal.

= Rs. `(100 xx 810)/135 = "Rs."  600`