The strength levels of a group of Martians follows Normal distribution with a mean of 75kgf and a std. dev. of 5kgf.
(a) How many Martians do you expect to meet before you find one with a strength level greater than 72 kgf?
(b) In a group of 5 Martians, what is the probability that exactly 4 Martians have strength levels greater than 72 kgf?
(c) 4 Martians are trying to open a huge stone door which will open only if all of their individual strength levels are greater than 72 kgf. What is the probability that they will open the door?
EDIT: Never mind I figured out (a) and (c). Still need help on (b), though. Thanks. I'll probably kick myself for not seeing it, but oh well.