Question 1210205
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At least 6 times means either all seven digits are the same or six of the seven are the same.<br>
(1) all 7 digits the same<br>
The digit can be any one of the 10 digits 0 to 9: 10 choices.<br>
There are 10 7-digit sequences containing a single digit 7 times.<br>
(2) 6 of the 7 digits the same<br>
(a) choose 1 of the 10 digits to be the one that occurs 6 times: 10 choices
(b) choose 1 of the other 9 digits to be the digit that is difference: 9 choices
(c) find the number of arrangements of the string AAAAAAB.  That number is<br>
{{{7!/((6!)(1!))=7}}}<br>
There are 7 ways to arrange those digits.<br>
Total number of 7-digit numbers with 6 of the digits the same: 10*9*7 = 630.<br>
Total number of 7-digit numbers with at least 6 digits the same: 10+630 = 640.<br>
ANSWER: 640<br>