The mean annual incomes of certified welders are normally distributed with the mean of $50,000 and a population standard deviation of $2,000. The ship building association wishes to find out whether their welders earn more or less than $50,000 annually. The alternate hypothesis is that the mean is not $50,000. If the level of significance is 0.10,what is the critical value?
A)+1.645
B)−1.282
C)±1.282
D)±1.645

Question

Quizplus · Accepted Answer

Since the alternate hypothesis is that the mean is not $50,000, this is a two-tailed test. The level of significance is 0.10, which means the alpha level is 0.05 (divided equally between the two tails). 
Using a z-table, the critical values for a two-tailed test with an alpha level of 0.05 are ±1.645. Therefore, the answer is D.

The Mean Annual Incomes of Certified Welders Are Normally Distributed