2013年新gre考试：gre数学考点之Conditional详解

Conditional

Probability of event A conditioned on the fact that event B has happened is called the conditional probability and written as P(AIB).

P(AIB)=Probability Both A and B happens/ Probability B happens.

Example:

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?

P(sum of faces is 9)=4/36=1/9.

P(face 5 turns up on the first try and sum is 9)=(1/6)*(1/6)=1/36.

P(face 5 turned up on first try given sum is 9)=(1/36)*(1/9)=1/4

Remember:

If P(AIB)=P(A),then two events A and B are independent, that is occurrence of one does not influence the other

以上就是GRE数学常考题总结，大家需要多加练习，总结易错点，进行集中突击。在考前，最好把错题都重看一遍，以免在考场上犯同样的错误。

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