There are y + 12 total balls in the bag. The probability of drawing a blue one is is 12/(y + 12), and the probability of drawing a yellow one is y/(y + 12). We're told that the probability of drawing a blue ball is less than 2/5, so
[tex]\dfrac{12}{y+12}<\dfrac25\implies30<y+12\implies y>18[/tex]
which tells us there must be at least 19 yellow balls in the bag.
