Conditional Probability of event A conditioned on the fact that event B has happened is called the conditional probability and written as P(AIB).& l" }7 j; ^/ C8 r- L
P(AIB)=Probability Both A and B happens/ Probability B happens.
" d$ Y4 B; ^% m( o Example:
: m# K3 [" C) f9 j A six-sided die with faces from 1 to 6 is rolled twice. What is the probability that the face 5 turned up on first try given that the sum of the two faces is 9?+ L, u1 F3 V {" c
P(sum of faces is 9)=4/36=1/9.
& D- |2 u: P, J P(face 5 turns up on the first try and sum is 9)=(1/6)*(1/6)=1/36.
5 w* Y; Z; h6 W, n. I P(face 5 turned up on first try given sum is 9)=(1/36)*(1/9)=1/4
* D) E {( F9 m3 x' w Remember:2 I; w7 T8 M w: k. A
If P(AIB)=P(A),then two events A and B are independent, that is occurrence of one does not influence the other |
发表于 2012-8-15 12:55:17
