Computer keyboard failures can be attributed to electrical defects or mechanical

Question

Computer keyboard failures can be attributed to electrical defects or mechanical defects. A repair facility currently has 25 failed keyboards, 8 of which have electrical defects and 17 of which have mechanical defects. (a) How many ways are there to randomly select 7 of these keyboards for a thorough inspection (without regard to order)? ways (b) In how many ways can a sample of 7 keyboards be selected so that exactly two have an electrical defect? 23800 ways (c) If a sample of 7 keyboards is randomly selected, what is the probability that at least 6 of these will have a mechanical defect? (Round your answer to four decimal places.)

Explanation / Answer

a) Number of ways of selecting 7 keyboards

= 25C7

= 480700

b) Number of required ways

= 8C2 * 17C5

= 173264

c) P(At least 6 with mechanical defects) = 0.2464

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