A quality control engineer finds that a sample of 100 light bulbs had an average life-time of 470 hours. Assuming a population standard deviation of σ = 25 hours, test whether the population mean is 480 hours vs. the alternative hypothesis < 480 at a significance level of a = 0.05. • Step 1: Ho : k = 480, Ha : p < 480. • Step 2: Choose a = 0.05 • Step 3: reject Ho if X< HOT 20.05 480 1.645- = 475.9 25 10 • Step 4: X = 470 < 475.9, therefore reject Ho.