Given:
Number of people having skin disorder =200
Number of people exposed to chemical C1=120
Number of people exposed to chemical C2=50
Number of people exposed to both chemical C1 and C2=30
(i)
Number of people exposed to chemical C1 but not chemical C2= Number of people exposed to chemical C1− Number of people exposed to both chemical C1 and C2
=120−30
=90
Hence, the number of individuals exposed to chemical C1 but not to chemical C2 is 90.
(ii)
Number of people exposed to chemical C2 but not chemical C1= Number of people exposed to chemical C2− Number of people exposed to both chemical C1 and C2
=50−30
=20
Hence, the number of individuals exposed to chemical C2 but not to chemical C1 is 20.
(iii)
Let U denote the universal set consisting of individuals suffering from skin disorder, A and B denote the set of individuals exposed to chemical C1 and C2 respectively.
∵n(U)=200,n(A)=120,n(B)=50 and n(A ∩ B)=30
∴n(A ∪ B)=n(A)+n(B)−n(A ∩ B)
=120+50−30
=170−30
=140
∴140 individuals are exposed either to chemical C1 or to chemical C2.