a. X be the number of stored radios with two slots has hypergeometric distribution
Given that "N=20, M=12, n=6."
b.
"P(X\\leq3)=P(X=0)+P(X=1)+P(X=2)+P(X=3)"
"P(X=1)={\\dbinom{12}{1}\\dbinom{20-12}{6-1} \\over \\dbinom{20}{6}}={12(56) \\over 38760}={672 \\over 38760}"
"P(X=2)={\\dbinom{12}{2}\\dbinom{20-12}{6-2} \\over \\dbinom{20}{6}}={66(70) \\over 38760}={4620 \\over 38760}"
"P(X=3)={\\dbinom{12}{3}\\dbinom{20-12}{6-3} \\over \\dbinom{20}{6}}={220(56) \\over 38760}={12320\\over 38760}"
"P(X\\leq3)={28 \\over 38760}+{672 \\over 38760}+{4620 \\over 38760}+{12320 \\over 38760}="
"={17640 \\over 38760}={147\\over 323}\\approx0.4551"
c. Calculate the mean and standard deviation of X.
"Var(X)=\\sigma^2=({N-n \\over N-1})\\cdot n\\cdot{M \\over N}(1-{M \\over N})="
"=({20-6\\over 20-1})\\cdot 6\\cdot{12 \\over 20}(1-{12 \\over 20})={504 \\over 475}"
"\\sigma=\\sqrt{{504 \\over 475}}\\approx1.03"
d.
"P(3.6<X\\leq4.63)=P(X=4)="
"={\\dbinom{12}{4}\\dbinom{20-12}{6-4} \\over \\dbinom{20}{6}}={495(28) \\over 38760}={13860\\over 38760}="
"={231\\over 646}\\approx0.3576"
e.
Moderately negative skewed.
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The records of an Italian shoe manufacturer show that 20% of the shoes are defective. Assume that selection of shoes follow a Bernoulli trial. a. If a manufacturer inspects 15 shoes randomly, what is the probability that at most two shoes are defective? b. If a manufacturer wants to find 6 non defective shoes, what is the probability that 12 shoes have to be inspected? c. Find the expected number of inspected shoes to find 6 non defective shoes.
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