Correct Answer - B
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(NuuS)=32, n(N) =30, n(S)=17`
We know that,
`n(NuuS)=n(N)+n(S)-n(NnnS)`
`implies32=30+17-n(NnnS)`
`impliesn(NnnS)=47-32=15`