Let n(A) and n(B) be the percentage of population in a city who read newspaper A and B respectively.
Therefore, n(A)=25, n(B)=20 and n(A∩B)=8
Now, we know that
n(A∩Bˉ)=n(A)−n(A∩B)
⇒n(A∩Bˉ)=25−8
⇒n(A∩Bˉ)=17
And,
n(Aˉ∩B)=n(B)−n(A∩B)
⇒n(Aˉ∩B)=20−8
⇒n(Aˉ∩B)=12
Therefore, percentage of those who read advertisements is
=30 of n(A∩Bˉ)+40 of n(B∩Aˉ)+50 of n(A∩B)
=10030×17+10040×12+10050×8
=1001390
Total persons who look into advertisement =13.9