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How many 3-digit numbers contain exactly one 1? Examples include 510 and 771.

 Apr 10, 2021
 #1
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a 1 in the hundred place: 9*9 (9 options for 10 and 1 place)

a 1 in the tens place: 8*9 (8 options for 100 and 9 optinos for 1 place)

a 1 in the ones place: 8*9 (8 options for 100 and 9 optinos for 1 place)

 

9*9+8*9+8*9=225

I hope this helped. :)))

 

=^._.^=

 Apr 10, 2021

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