Question

the difference between CI and Si on rupees 8400 for 2 years is rupees 21 at the same rate of interest per year find the rate of interest
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Answer 1

Step-by-step explanation:

Difference = Principal (r/100)2

Answer 2

Concept

Compound interest is the interest calculated on the aggregate of principal and aggregate interest and simple interest is the interest calculated on the amount directly on the principal amount. The formula for calculating compound interest is P$(1+r)^{n}$-P and the formula for calculating simple interest is P*R*T.

Given

The difference between compound interest and simple interest is 21 and the rate of interest is same.

To find

The rate of interest.

Explanation

According to question we can solve for interest as under:

8400$(1+r/100)^{2}$-8400-8400*r/100*2=21

8400[$(1+r/100)^{2}$-1-2r/100]=21

8400[1+$r^{2} /10000$+2r/100-1-2r/100]=21

8400[1+$r^{2}/10000$-1]=21

8400$r^{2} /10000$=21

$r^{2}$=210000/8400

$r^{2}$=25

r=5

Hence the rate of interest for the amount 8400 rupees is 5 percent.

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