<PRE><B>Question 75535</B>
Four letters and envelopes are addressed to four different people. If the letters are randomly inserted into the envelopes, what is the probability that(a) exactly one is inserted in the correct envelope:
P(success)=1/4
P(one correct of four)= 4C1 (1/4)^1(3/4)^3 = 4(27/256)=0.421875
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(b) at least one is inserted in the correct envelope
P(at least one) = 1 - P(none correct)
= 1 - 4C0(1/4)^0(3/4)^4 
= 1 - 1*1*81/256 
= 1 - 0.316
= 0.6835
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Cheers,
stan H.
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