Vic has 40 marbles, all are either yellow or blue. He gives half his yellow marbles to mark. After this Vic has 27 marbles left. How many blue marbles does he have?

40-27 is the amount he has given away which equals 13 which if that is half of the yellow marbles so that means he HAD double that so he had 26 yellow ones in all. 40-26 must be the amount of blue marbles he had so he had 14 blue marbles.

14 blue marbles. 40-27=13 and 13 is half of yellow so 13+13=26 and 40-26=14 blue marbles