Question

There are 200 individuals with a skin disorder of these, 120 had been exposed to the chemical $C_1,50$ to chemical $C_2$ and 30 to both the chemicals $C_1$ and $C_2$.
The number of individuals exposed to chemical $C_2$ but not chemical $C_1$ is

• A. 80
• B. 20
• C. 50
• D. 10

Answer 1

Answer: (B)

From the above diagram, we have
and so,
$B=(B-A)\cup (A\cap B)$
$n(B)=n(B-A)+n(A\cap B)$
( since, $B-A$ and $A\cap B$ are disjoint)
or $n(B-A)=n(B)-n(A\cap B)$
$=50-30=20$
Thus, the number of individuals exposed to chemical $C_2$ but not to chemical $C_1$ is 20 .