新GRE数学重要考点：Conditional

各个击破新GRE数学重要考点，今天小编为大家整理的是Conditional相关的内容。

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