A manufacturer takes two simple random samples from a large batch of rechargeable batteries. In sample A, 9 of 150 batteries fail a capacity test. In sample B, 4 of 60 batteries fail the test.
Calculate the estimated failure proportion from each sample.
A manager says, "Sample B proves that the batch has become less reliable." Criticise this statement.
The two samples are combined. Calculate the estimated failure proportion for the combined sample.