Discussion Forum



1)

With rate of simple interest, the ratio of principal and amount for a certain period of time is $4:5$. After 3 years, with the same rate of interest, the ratio of the principal and amount becomes $5:7$. The rate of interest is


A) 4%

B) 6%

C) 5%

D) 7%

E) 9%

Answer:

Option C

Explanation:

Case I

$SI$ $=5x-4x$ $=x$

$x$ $=\frac{(4x\times R\times N)}{100}$

$N$ $=\frac{25}{R}$ Years

Case II

$N$ $=\frac{25}{R}+ 3$ $=\frac{(25+3R)}{R}$

$SI$ $=7y-5y$ $=2y$

$2y$ $=\frac{5y\times R\times (25+3R)}{100R}$

R = 5%