A bag has 10 balls. Six balls are drawn in an attempt and replaced. Then another draw of 5 balls is made from the bag. The probability that exactly two balls are common to both the draw is

The total number of ways of making the second draw is 10C5.The number of draws of 5 balls containing 2 balls common with first draw of 6 balls is 6C2 4C3. There fore, the probability is 6C24C3 10C5=521