The life spans of a computer manufacturer’s hard drives are normally distributed, with a mean of 3 years 6 months and a standard deviation of 9 months. What is the probability of a randomly selected hard drive from the company lasting between 2 years 3 months and 3 years 3 months? Use the portion of the standard normal table below to help answer the question.

z
Probability
0.00
0.5000
0.23
0.5910
0.33
0.6293
0.67
0.7486
1.00
0.8413
1.33
0.9082
1.67
0.9525
2.00
0.9772
32%
37%
42%
95%

Question

The life spans of a computer manufacturer’s hard drives are normally distributed, with a mean of 3 years 6 months and a standard deviation of 9 months. What is the probability of a randomly selected hard drive from the company lasting between 2 years 3 months and 3 years 3 months? Use the portion of the standard normal table below to help answer the question.

z
Probability
0.00
0.5000
0.23
0.5910
0.33
0.6293
0.67
0.7486
1.00
0.8413
1.33
0.9082
1.67
0.9525
2.00
0.9772
32%
37%
42%
95%

mhanifa · Answer

1. Find z-scores for two points. Use formula:
z=(x−μ)/σ
2. Find the difference of them
3. Convert the number to percent value (multiply z-sore difference by 100%)