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have one or more "7"

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have one or more "7"

by sanju09 » Sat Aug 14, 2010 2:21 am
What is the probability that a 3-digit positive integer picked at random will have one or more "7" in its digits?
(A) 271/900
(B) 27/100
(C) 7/25
(D) 1/9
(E) 1/10


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by shibal » Sat Aug 14, 2010 7:43 am
ways of obtaining a three digit number 9*10*10 = 900ways
ways of obtaining a three digit number WITHOUT 7 is 8*9*9 = 648 ways

1- (648/900) = 252/900 = 7/25
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