



 
Hi David, Look at the response I just sent to Theresa about four digit numbers made from 1234. Repeat my solution using the digits 1259. How many did you get? Every 4 digit number in your list has an "almost twin", one where the 1 and 2 are reversed, for example 1572 and 2571. Now replace each 2 with a 1 and these do become twins 1571 and 1571. Thus the number of 4 digit numbers that can be formed from 1159 is half the number that can be formed from 1259. I hope this helps,  


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