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, 9 of which have electrical defects and 16 of which have mechanical defects How many ways are there to randomly select 7 of these keyboards for a thorough inspection (without regard to order)? 269023 (a) x ways (b) In how many ways can a sample of 7 keyboards be selected so that exactly two have an electrical defect? ways (e) If a sample of 7 keyboards is randornly 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

Result:

a).

25C7 = 480700 ways

b).

9C2 *16C5 = 36*4368 = 157248 ways

c).

atleast 6 mechanical defect = 6 mechanical defect or 7 mechanical defect

Number of ways 6 mechanical defect or7 mechanical defect = 9C1*16C6 +9C0*16C7

=9*8008+1*11440 = 83512

The required probability =83512/480700

=0.17373

=0.1737 ( four decimals)

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