ranga41 wrote:

7/10*6/9 = 7/15

hows the second draw probability 6/9 here? wont it depend on first draw. I mean if:

A) first draw resulted into one of the stamp in peter's collection, this probability would be : 7/9

B) first draw did not result into perter's collection stamps, second draw probability would be:

6/9

As first draw probability remains same, the total probability would be:

7/10 * 7/9 + 7/10 * 6/9 or

91/90
Guess ans to this question depends/changes on if:

- both stamps are drawn "together"

- stamps are drawn one after another.

The ans will vary based on the two.