What is the probability that all the ones he bought are good

A box of 200 printer cartridges is used to stock the shelves. 10 of the cartridges are defective.

i) A customer buys 15 cartridges from the 200. What is the probability that all the ones he bought are good?
ii) A second customer buys 15 more cartridges from the same shelf. What is the probability that he got all good ones too, assuming the first customer got all good ones?

i) The probability that all 15 are good is the probability that any one is good ((200-10)/200) or .95, raised to the 15th power. That works out to be about 46%.

ii) If the first customer got all good ones, then the probability of any remaining cartridges being good is (190-15)/(200-15), or a little bit less than .95. To get the probability that all 15 are good you would raise that slightly less than .95 value to the 15th power, which works out to be about 43%.

i) The probability that the first cartridge bought is good is 190/200.
The probability that the 2nd cartridge is good is: 189/199
The prob the third cartridge is good is : 188/188.
Etc.

2) Continue as is 1.

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