The probability of picking blue is the number of blue marbles/ total marbles.
For the first pick there are 2 blue marbles and 9 total marbles so the probability of picking blue would be 2/9
After picking the first marble there would be 1 blue marble left and 8 total marbles. The probability of picking the blue marble would be 1/8
To find the probability of picking both, multiply the probability of each one by each other:
2/9 x 1/8 = 2/72, which reduces to 1/36
The answer is 1/36
