Statistics "sample probability" HELP?!?

Question

In a sample of 154 cartridges from a certain lot, 38 were found to be contaminated and 116 were "clean". If you randomly select 4 of these 154 cartridges, what is the probability that all 4 will be clean?
The probability that all four cartridges will be "clean" is: ______ (round to four decimal places).

Answer 1

(116*115*114*113) / (154*153*152*151) = .3178

So, a sample of four is not a good test unless you like to have 20+% defects.

Answer 2

Use the combination formula.
P(clean=4, cont=0)= C(116,4)*C(38,0)/C(154,4) = 7160245*1/22533126=0.3178