You have 9 bills all in all in your wallet. From the probability , P($10 then $1), you are to pick $10 bill first out of the 9. The probability of doing so is 2/9. Then you have 8 bills left. The probability of picking $1 is 3/8. The final probability is the product of the two probabilities. The answer is therefore, (2/9) x (3/8) or equal to 1/12.
