The solution is: B) 2/3

If you missed the Maths Week problem last week the question has been repeated below. 

You have three bags, each containing two marbles. Bag A contains two white marbles, Bag B contains two black marbles, and Bag C contains one white marble and one black marble. You pick a random bag and take out one marble, it is a white marble. What is the probability that the remaining marble from the same bag is also white?

A) 1/2

B) 2/3

C) 1/4

D) 1/3