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.
(In reply to
re(2): Partial Solution  ? with no answer of my own by tomarken)
I just got done brute forcing it myself. 72 out of 504 combos are divisible by 7 which is 1/7.
For part b, though some combos work in more than one way (789 forms two numbers that work for example  798 and 987) and more than expected don't work at all. Of the 84 combinations, only 54 have a working permutation. 54/84 = 9/14 which is quite a bit less than 6/7

Posted by Jer
on 20060425 13:40:54 