Question

The life expectancy of Timely brand watches is normally distributed with a mean of 4 years and a standard deviation of 8 months. Ninety-five percent of the watches will have a life expectancy of at least how many months

Answer 1

Answer:

63.68 months

Step-by-step explanation:

We solve this question with z score formula

z = (x-μ)/σ, where

x is the raw score ???

μ is the population mean = 4 years

Since the final answer would be in months, we would convert mean to months

= 1 year = 12 months

4 years = x months

= 12 × 4 = 48 months

σ is the population standard deviation = 8 months

z = the z score for 95% confidence interval = 1.96

1.96 = x - 48/8

1.96 × 8 = x - 48

15.68 = x - 48

x = 15.68 + 48

x = 63.68 months