



 
Hi Rob. There are four digits on the combo: xxxx. In each case, the xx component is any number, but I bet you would have remembered if there were more than 2 sixes, so I think we only need to consider the two digit values that don't have a six in them. Those are: 0005,0715,1725,2735,3745,4755,57,58,59,7075,7786,8795,97,99. There are 19 eliminated numbers here. You would probably remember as well if the other two digits were twins too. So we can eliminate 00, 11, 22, ... 99. That's nine more gone. Thus, you have 100  28 = 72 twodigit numbers together with 6 positions for each. That means 6 x 72 = 432 possible combinations. I'm not going to list them for you, but now you can see how to do it: For each of the 72 numbers, try the six permutations Good luck!  


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