Simulation: Rivets

[ericataylor]

Hi, I've been having some trouble with this question:

A company that manufactures rivets believes the shear strength of the rivets they manufacture follows a Normal model with a mean breaking strength of 950 pounds and a standard deviation of 40 pounds.

Part A asks about percentages; I need help with Part B:

You're trying to improve the rivets and want to examine some that fail. Use a simulation to estimate how many rivets you might need to test in order to find three that fail at 900 pounds (or below).

Maybe it's because I'm not completely sure about "breaking strength" - is it, basically, that over 950 pounds, their rivets will probably break? I think so, but I'm not sure. Anyway, I cannot figure out how to simulate this. Normally I like doing simulations, but this one is so hard for me. I was thinking that I could randomly generate numbers 0-9, with 0-7 representing ones that didn't break and 8-9 representing ones that did. I really don't feel that's right, though. Am I on the right track, or totally missing the point?

 

[tkhunny]

(900-950)/40 = -1.25

How much Normal probability is below that value?

If the probability is 100% (which it isn't), you need 3 to expect to find 3.
If the probability is 50% (which it isn't), you need 6 to expect to find 3.
If the probability is 5% (which it isn't), you need 60 to expect to find 3.

Getting the picture?