Among the 24 invoices prepared by billing department 4 conta

Among the 24 invoices prepared by billing department, 4 contain errors while the others do not. If we randomly check 2 of these invoices, what are the probabilities that both will contain errors; neither will contain an error

Solution

here we get an error with prob 4/24 and we get an error with prob (1-4/24)=20/24

two items are drawn

a) P(both contain error)=(4/24)*(4/24)=0.028

b) PP(both item is without error )=(20/24)*(20/24)=0.69