math foundations 20
posted by Ayane .
How do I solve normal distribution word problems? Ex
A manufacturer offers a warranty on it's coffee makers. The coffee makers have mean lifespan of 4.5 years, with standard deviation of 0.7 yeaes. For how long should the coffee makers be covered by the warranty, if the manufacturer wants to repair no more than 2.5% of the coffee makers sold?

you want x such that P(Z<x) = 0.025
That means that x must be more than 1.96 std below the mean. In this case, that's 3.128 years.