In: Statistics and Probability
A railway company used 2 types of wheel mounts that differ in the way they handle track irregularities: type A and type B. The following data gives the repair records for 2 types over a 1 year period:
| # of cars | # needing service | |
| Type A | 150 | 20 | 
| Type B | 180 | 18 | 
Test for the difference between population proportions PA and PB.Use α = 0.02.