B denote the event of a sum of 7 on the two die, and D the event that the

sum of the two die is odd.

If B has occured then of necessity so has D as 7 is odd.

The even (B and D) means both events have occured, which always has the

same truth value as B, so in this case:

P(B and D)=P(B)

Alternativly draw a Venn diagam, then B is entirly enclosed withing D, and

the event (B and D) is represented by the area of overlap of B and D, which

in such a case is B.

Drawing a Venn diagram will also show why P(B or D)=P(D) when B is contained in

D.

RonL