A horticulturist wishes to estimate the true mean growth of seedlings in a large timber plot last year. A random sample of 20 seedlings is selected and the one-year growth for each of them is measured. The sampled seedlings have a mean growth of 5.6 cm and a standard deviation of 1.5 cm. One-year seedling growth is known to follow a normal distribution with standard deviation 2.0 cm. We wish to conduct a hypothesis test at the 10% level of signiﬁcance to determine whether the true mean one-year seedling growth diﬀers from 6.0 cm. The critical region for the test is:

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