Question

A bought 10 books at Rs 1000. The shop increased the cost of books because of which A only bought 9 books next month. This time , it cost him Rs 990. What is the difference between the new cost and the old cost of the book?
Assume he bought the same books in the next month as well.

• A. Rs 5
• B. Rs 15
• C. Rs 10
• D. Rs 20

Answer 1

The correct option is C Rs 10

In the first month,
A bought 10 books at Rs 1000
$\Rightarrow$ Cost of 1 book = $\frac{1000}{10}=Rs100$

In the second month,
A bought 9 books at Rs 990
$\Rightarrow$ Cost of 1 book = $\frac{990}{9}=Rs110$

$\therefore$ The difference in the new cost and the old cost = Rs 110 - Rs 100 = Rs 10