Hi, Re:TY,
The display below are the possible outcomes rolling a pair of dice
Only one of the outcomes is >9 'and' is a 12, thus the 1/36
There are 6 possible outcomes >9 and therefore the 6/36
P(A|B) = P(A and B)/P(B)
P(12|>9) = = 1/6
___1_2_3__4__5__6
1|_2_3_4__5__6__7
2|_3_4_5__6__7__8
3|_4_5_6__7__8__9
4|_5_6_7__8__9_10
5|_6_7_8__9_10_11
6|_7_8_9_10_11_