Acompany has 200 machines. each machine has 12% probability of not working.1) if you were to pick 40 machines randomly, the probability that 5 would not be working 2) the probability that all would be working 3) and the probability that at least one machine would be working

1) This probability is given by

... C(40,5)·0.12⁵·0.88³⁵ ≈ 0.18665 . . . . . where C(n, k) = n!/(k!(n-k)!)

2) This probability is given by

... 0.88⁴⁰ ≈ 0.00602

3) This is the complement of the probability that all have failed.

... 1 - 0.12⁴⁰ ≈ 1.0000

take the logarithm of both sides (the base of the log doesn't matter):

apply the exponent property - this says that :

distribute the log terms on both sides:

group like terms together:

divide through both sides by the coefficient on :

you can do some additional rewriting here using the properties of the logarithm to simplify things if you like: