Question

In a school library, the ratio of Science to English books is 10 ∶ 13. If there are 400 Science books and due to increase in demand of Science books, few Science books are added by school authority and the ratio becomes 25 ∶ 26. What is the number of Science books added?

• A. 50
• B. 100
• C. 120
• D. 80

Answer 1

Answer:

B. 100

Given:

Initial ratio of Science to English books = 10 : 13

Number of initial Science books = 400

Ratio after addition of Science books = 25 : 26

Formula:

Number of Science books added = Final number of Science books - Initial number of Science books

Solution:

From the given initial ratio, 10 parts of the ratio represent 400 books.

⇒ Each part represent $\frac{400}{10}$ = 40 books

⇒ So, the number of English books = 13 parts = $40\times{13}$= 520 books

Now, the ratio of Science to English books, after addition of Science books, is 25 : 26.

Given, number of English books remain the same (as no addition in English books).

1 part of the ratio is therefore equivalent to $\frac{520}{26}$ = 20 books.

⇒ Hence, after addition, the number of Science books = 25 parts = $20\times{25}$ = 500 books

Number of Science books added = Final number of Science books - Initial number of Science books

⇒ 500 - 400

⇒ 100

Therefore, the number of Science books added is 100.