Question

If the compound interest on a certain sum for 2 years is rs. 21. What could be the simple interest

Answer 1

Answer:

20 could be the simple interest.

Step-by-step explanation:

Let the principal is x and the rate of interest is r% annually.

The simple interest after 2 years will be $\frac{2rx}{100}$.

The compound interest after 2 years is $\frac{x2r}{100} + \frac{xr^{2} }{10000}$.

As per the given scenario, $\frac{x2r}{100} + \frac{xr^{2} }{10000}$ = 21.

$\frac{xr}{100} [2+\frac{r}{100} ] = 21$.

If we break 21 as 10 + 10 + 1, then it gives two equal parts 10. We can compare this 10 as $\frac{xr}{100}$.

Hence, thus 20 could be the simple interest.

Answer 2

Answer:

₹20

Step-by-step explanation:

let just assume principal be 100.

Then according to formula of CI, interest will be

p(1+r/100)^2 - p = 100(1+r/100)^2 - 100 = 21

(1+r/100)^2 = 1.21

1+r/100 = 1.1 ---> r/100 = 0.1

hence r = 10%.

Then SI will be PRT/100

= (100×10×2)/100

=20.