CDS Model Paper 4 Mathematics

Let N= National savings certificates
S= Shares
Total no. of persons =32
No. of persons who invest in National
savings certificates =30
No. of persons who invest in shares =17
Therefore
n(N∪S)=32,n(N)=30,n(S)=17
We know that,
n(N∪S)=n(N)+n(S)−n(N∩S)
⇒ 32=30+17−n(N∩S)
⇒ n(N∩S)=47−32=15