In how many ways can 2 televisions be selected from 15?
"\\binom{15}{2}={15! \\over 2!(15-2)!}={15\\cdot 14 \\over 1\\cdot 2}=105" In how many ways can 0 defective televisions be selected from 4?
"\\binom{4}{0}={4! \\over 0!(4-0)!}=1" In how many ways can 2 non-defective televisions be selected from 11?
"\\binom{11}{2}={11! \\over 2!(11-2)!}={11\\cdot 10 \\over 1\\cdot 2}=55" Compute the probability that both televisions work
"P(both\\ work)={\\binom{4}{0}\\binom{11}{2} \\over \\binom{15}{2}}={1\\cdot 55 \\over 105}={11 \\over 21}\\approx0.5238" What is the probability at least one of the two televisions does not work?
"P(at\\ least \\ 1\\ does\\ not\\ work)=1-P(both\\ work)=""=1-{11 \\over 21}={10 \\over 21}\\approx0.4762"
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