I have the question
Computer keyboard failures can be attributed to electrical defects or mechanical defects. A repair
facility currently has 25 failed keyboards, 6 of which have electrical defects and 19 of which have
mechanical defects
A) In how many ways can a sample of 5 keyboards be selected so that exactly two have an electrical defect?
B) If a sample of 5 keyboards is random selected, what is the probability that at least 4 of these will have a mechanical defect?
For A – I know i have to use combinations, but i'm not sure what the numbers are.
Could anyone begin to point me in the right direction? Thanks!
Best Answer
B) If a sample of 5 keyboards is random selected, what is the probability that at least 4 of these will have a mechanical defect?
$$P = \frac{{19\choose 4}+{19\choose 5}}{25 \choose 5}$$