Question

The pH of a stream near a sugar factory is measured once a year to monitor whether waste water from the factory is decreasing the pH of the stream. The pH of the stream before the factory was built was 6.9 with a standard deviation of 0.2. A year later, after operations at the factory began, the pH was measured as 6.5 with a standard deviation of 0.1. If the null hypothesis, Ho, is that the pH of the stream is the same after the factory was built as it was before the factory was built, what is the alternate hypothesis, Ha? If we want to determine at the 95% confidence level whether the pH is significantly less after the factory was built, what critical z value (zcrit) must we use when determining if z is less than zarit? Assume the standard deviation is a good estimate of the population standard deviation (o) Number

Answer 1

The null hypothesis

H0: $\mu$ = $\mu$0

The alternative hypothesis

Ha: $\mu$ < $\mu$0

This is left tailed test.

From Z table,

z critical value at 0.05 significance level Z_crit = -1.645