Find the probability that a normal standard variable is less than or equal 0

Problem

1. Find the probability that a normal standard variable is less than or equal 0.

2. Given a normal distribution with  = 3 and  = 0.5, find the probability that X assumes

a value less than or equal 2.3.

Problem

9 friends decide to “go for a drink” after an exam. What is the probability that the waitress will refuse to serve alcoholic beverages to only 2 minors if she randomly checks the IDs of 5 students from among 9 students of which 4 are not of legal age?