Problem
The amount of time a certain brand of light bulb lasts is normally distributed with a mean of 1800 hours and a standard deviation of 95 hours. Out of 530 freshly installed light bulbs in a new large building, how many would be expected to last between 1620 hours and 1920 hours, to the nearest whole number? Statistics Calculator Answer: Submit Answer attempt 1 out of 2
Solution
Step 1 ：\( z_1 = \frac{1620 - 1800}{95} = -1.8947 \)
Step 2 ：\( z_2 = \frac{1920 - 1800}{95} = 1.2632 \)
Step 3 ：\( P(z_1 < Z < z_2) = 0.7933 \)
Step 4 ：\( N = 530 * 0.7933 = 420.546 \)
