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Unformatted text preview: ning digit different from the other two?
Using the probability method
N = 1,000 – 100 = 900
P1 = 1/10*8/10 = 8/100
P2 = 8/10*1/10 = 8/100
P3 = 8/10*1/10 = 8/100 SP = 8/100+8/100+8/100 = 24/100
N*P = 900*24/1,000 = 216
The answer is (E) 4 For calculating P we need this time to understand that again there are three possible P's - but with a twist. In
P1 the first digit is not important, let's say we choose 1. The second digit has to be also 1 but we have 10
digits to choose from (0-9) so the probability is 1/10 and the last digit has to be different than 1 but we
cannot choose zero so 8/10.
In P2 the first digit is not important (let's say we choose 8) but the second digit can't be 8 and can't be zero
so 8/10 and the last digit has to be 8 so 1/10.
In P3 the same logic is used. The first digit is not important (let's say we choose 5) – in the second digit we
can choose 8 out of 10 digits (we can't choose 5 which we've already chosen, nor can we choose 0) so –
8/10 and in the last digit we need to choose the second digit exactly so 1/10.
Written by KillerSquirrel – 2007 5...
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This document was uploaded on 02/28/2014.
- Fall '13