probability = no of outcomes / total outcomes
First draw = no of blue mables / total mables = 3 / (4 + 3 + 3) = 3/10
For the second draw, since there was no replacement of the first draw, the blue mables has reduced by one, and the total mables has reduced by one.
Second draw = no of remaining blue mables / total remaining mables = 2/9
Probability for both draws = 3/10 x 2/9 = 1/15
