so your mean would be 24.5, and we are interested in the area below 20, so you would have:
so 0.0166 coils would be inadequate
A manufacturer needs coil springs that can stand a load of at least 20.0 pounds. The supplier can provide coil springs that, on average, can stand a load of 24.5 pounds with a standard deviation of 2.1 pounds. If we can assume that the distributions of these loads can be approximated with normal distributions, determine the percentage of unsatisfactory coil springs that would be obtained from the supplier.
I am having a difficult time with this one. Can anyone help?