SETS 1

In a certain school, 160 students take either Chemistry or biology. 130 take chemistry and 100 take both subjects. Find those who take biology only.

Solution

In most cases, OR stands for union whereas AND/BOTH, stands for intersection.

Let Chemistry = n(C), Biology = n(B).

n(C)= 130 ,

n(B)= ?

n(CuB) = 160,

n(CnB)= 100

Solution

n(CuB) = n(C) + n(B) - n(CnB)

160  =  130 + n(B)  – 100

160  =  n(B) + 30

160 - 30  =  n(B)

n(B)= 130

physics only = n(B) – n(CnB)

                    = 130 – 100

                    = 30 

Hence those taking only biology are 30.    

TRY THIS………….

In a certain school, 185 students take either Chemistry or French. 160 take chemistry and 130 take both subjects. Find those who take French only.