probability

Probability Level 4

There are 6 bags, each with 5 balls. Each bag has a different number of white balls (from 0 to 5). One bag is randomly chosen, and 2 balls are randomly drawn from it. Given that both balls are white, the probability that all the balls in the bag are white is $\frac{a}{b}$ with a and b relatively prime , then find the value of $a \times b$ .