Question

There are 5 books on Mathematics and 6 books on Physics in a book shop. In how many ways can a student buy : 

(i) A Mathematics book and a Physics book?

(ii) Either a Mathematics book or a Physics book?

Answer 1

(i) Given, 

There are 5 books of mathematics and 6 books of physics. 

In order to buy one mathematics book number of ways are ⁵C₁ similarly to buy one physics book number of ways are ⁶C₁ 

Hence,

The number of ways a student buy a Mathematics book and a Physics book is ⁵C₁ × ⁶C₁ 

= 5 × 6 

= 30 

(ii) Given,

There is a total of 11 books, so in order to buy either a Mathematics book or a Physics book it means that only one book out of eleven is bought. 

Hence,

The number of ways in which a student can either buy either a Mathematics book or a Physics book is ¹¹C₁ = 11