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 Three from Nine (Posted on 2006-04-25)
Nine marbles numbered 1 to 9 are placed in a barrel and three are drawn out, without replacement. Determine -:

1. The probability that the three digit number formed from the marbles in the order drawn is divisible by (a) Five (b) Seven (c) Nine.
2. The probability that a three digit number can be formed by rearranging the marbles drawn, that is divisible by (a) Five (b) Seven (c) Nine.

 No Solution Yet Submitted by Vernon Lewis Rating: 3.5000 (4 votes)

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To be divisible by 5, the last digit must be 5 (there is no 0). So the first 2 digits cannot be 5.

Prob. of 1'st digit not equal to 5 = 8/9

prob. of 2'nd digit not equal to 5 = 7/8

prob. of 3'rd digit equal to 5 = 1/7

result is 8/9 * 7/8 * 1/7  =  1/9

 Posted by ruti on 2006-05-01 16:26:19

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