Out of 100 jobs vacant at some software company,30 jobs are class 1,and 70 jobs are class 2.Sample of 30 jobs are taken,then find the probability that
a)There will be exactly 12 jobs of class 1,
b)At the most 2 jobs on class 2.

a). Find total number of ways to pick 30 from the 100.
Find the total number of ways to pick 12 from class 1 and the rest from class 2.

Divide the second probability by the first.

b) Find total number of ways to get 2 from class 2, then 1 from class 2 and none from class 2. Add them all and divide by the total number you can pick (30 out of 100).