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How many 3-digit numbers contain exactly one 1 and exactly one 2?

 Aug 28, 2021
 #1
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12x

21x

x12

x21

1x2

2x1        6 ways for 1 and 2 to pbe in the number   the 'x' can be any of the remaining 8 numbers  (3 4 5 6 7 8 9 0)

 

6 * 8 = 48

 Aug 28, 2021
 #3
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*** EDIT ****

SInce you probably do not want leading zeroes in your 3 digit number

x 21     and   x 12   would not be on the list

 

48 -2 = 46 numbers    as Guest below computed

Guest Aug 28, 2021
 #2
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102  120  123  124  125  126  127  128  129  132  142  152  162  172  182  192  201  210  213  214  215  216  217  218  219  231  241  251  261  271  281  291  312  321  412  421  512  521  612  621  712  721  812  821  912  921  >>Total permutations = 46 such numbers.

 Aug 28, 2021

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