SETS B8

In a certain school, 200 students take either Chemistry or physics. 130 take physics and 100 take both subjects. Find those who take Chemistry only.

Solution

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

Let Chemistry = n(C), physics = n(P).

n(P)= 130 ,

n(C)= ?

n(CuP) = 200,

n(CnP)= 100

Solution

n(CuP) = n(C) + n(P) - n(CnP)

200  =  n(C) + 130 – 100

200  =  n(C) + 30

200 - 30  =  n(C)

n(C)= 170

Chemistry only = n(C) – n(CnP)

                         = 170 – 100

                         = 70 

Hence those taking only Chemistry are 70.      

TRY THIS......

In a certain school, 260 students take either Chemistry or physics. 140 take physics and 120 take both subjects. Find those who take Chemistry only.