Question

The life-span of a certain brand of car battery is normally distributed, with a mean of 2 years and standard deviation of 0.5 years.

a. what proportion of battery will last shorter than 1.7 years?

b. what proportion of battery will last longer than 2.7 years?

c. what proportion of battery will last between 1.5 years and 2.5 years?

d. the company wishes to allow only 10% claim from warranty, what is the warranty in months?

e, later 20% of customers claims from warranty. assuming that the mean has not changed, calculate the new standard deviation of the life-span of the battery.

Answer 1

For a. Do you know how to calculate the z-value so you can use a standardised table for the normal distribution

Answer 2

yes i do. just wanna check answers

Answer 3

What was your answer for a ?

Answer 4

@phdamage Do you have any answers you can post for checking?

Answer 5

sorry was away . a) 0.27425. b) 0.08076. c) 0.68268.
im not sure how to do d and e

Answer 6

@satellite73 can you cross check my answer? :x

Answer 7

a) .4761
= P ( z < -.6) = .5 - .0239
b) and c) are correct!

Answer 8

@phdamage You should partial your question into many posts, will attract more helpers :)