Question

A interest of ₹ 8000 and B intest ₹ 11000 at the same rate at the end of 3 years ,B gets ₹ 720 intrest than A .Find the rate of intrest

Answer 1

Required formula:

$\boxed{ \tt {\pink{S.I. = \frac{PRT}{100} } }}$

$: \implies \sf \red{A \: invested = Rs. 8000} \\ : \implies \sf \red{B \: invested = Rs. 11000}$

Time period of investment for both A & B, T = 3 years

Let the rate of interest in both the investment be “R”% and the interest earned by A and B be denoted as “Ia” & “Ib” respectively.

Interest earned by A after 3 years:

$\tt { : \implies \pink { Ia = \frac{8000 \times R \times 3 }{100} = 240R - - - - - (i)}}$

And,

Interest earned by B after 3 years:

$\tt { : \implies\pink{Ib = \frac{11000 \times 3 \times R}{100} = 330R - - - - (ii)}}$

It is given that at the end of 3 years the interest earned by B is Rs. 720 more than the interest earned by A, so we can write the equation as,

$\sf{Ib = Ia + 720} \\ \sf{⇒ 330R = 240R + 720 - - [substituting \: values \: from \: (i) \: and \: (ii)]} \\ \sf{⇒ 90R = 720} \\ \sf{⇒ R = \sf{\frac{720}{90}}} \sf{⇒ R = 8\%}$

Thus, the rate of interest is 8%.