Question

20 copies of a book can be purchased for a certain sum payable at the end of 6 months and 21 copies for the same sum in ready cash. Find the rate of interest.

Answer 1

Given :

Number of copies purchased = 20

Number of months = 6 months

Same number of copies = 21 copies

To find :

Rate of interest = ?

Solution :

Let we assume be the price of 1 book  is X

For 20 books payable amount after 6 months is

$Payable\ amount = Principal\times \frac{rate\times time\ period + 100}{100}$

$= 20X + \frac{X\times\ rate}{10}$

Since 20 books paid in cash -

So, Total price is 21X

And,

Cash price of 21 copies is same as interest of 20 copies

So

$20X + \frac{X\times rate}{10} = 21X$

$X = \frac{X\times rate}{10}$

X = 10%

Therefore, the rate is  10%

Hence the rate of interest is 10%

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