Homework SourseThis is a probability question The lifetimes of certain type
This is a probability question
| The lifetimes of certain types of car battery are normally distributed with a mean of 1248 days | ||||
| and a standard deviation of 185 days. If the supplier guarantees them for 1080 days, what | ||||
| proportion of batteries will be replaced under guarantee? |
Solution
Normal Distribution
Mean ( u ) =1248
Standard Deviation ( sd )=185
Normal Distribution = Z= X- u / sd ~ N(0,1)
P(X < 1080) = (1080-1248)/185
= -168/185= -0.9081
= P ( Z <-0.9081) From Standard Normal Table
= 0.1819 ~ 18.19% proportion rate are replaced
