Sunday Times Teaser 2594 – Just Enough
by Andrew Skidmore
Published: 10 June 2012 (link)
I have two identical bags of balls, each containing two reds, two yellows and two blues. Blindfolded throughout, I remove just enough balls from the first to be sure that the removed balls include at least two colours. I place these balls in the second bag. Then I remove some balls from the second bag and put them in the first: I move just enough to be sure that the first bag will now contain at least one ball of each colour.
What (as a percentage) is the probability that all the balls left in the second bag are the same colour?