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Three from Nine (Posted on 2006-04-25) Difficulty: 3 of 5
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)

Comments: ( Back to comment list | You must be logged in to post comments.)
Some Thoughts re(2): Partial Solution - ? with no answer of my own | Comment 6 of 12 |
(In reply to re: Partial Solution - ? with no answer of my own by Leming)

If the first two numbers total to 9 (like 3 and 6), you can always make the third digit 9 to preserve the divisibility by 9.  However, you are correct to have concerns, I was incorrect as you and Jer have shown.

I just did a "brute force" on the numbers in an excel spreadsheet and did find that the probability that the number will be divisible by 7 is 1/7.  Although I'm still perplexed as to how to explain why...


  Posted by tomarken on 2006-04-25 13:31:25
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