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  4. There are 200 individuals with a skin disorder of these, 120 had been exposed to the chemical C1, 50 to chemical C2 and 30 to both the chemicals C1 and C2. The number of individuals exposed to chemical C2 but not chemical C1 is

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Q. 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

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Solution:

image
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 .