Ans a. 100
Exp:-
Suppose no. Of voters =100
So Promised to vote P =40
Promised to vote Q=60
Then 15% of the voter promised to vote p went back and voted for Q = 15% of 40= 6
Rest out of 40 voted for P=34
similarly, 25% of 60 voted for P= 15
Rest out of 60 voted for P=45
So voted for P= 49
So voted for Q=51 voters
Difference between votes 51-49=2
So, no of voters=100