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How many 3-digit numbers have the property that the units digit is at least twice the tens digit plus 5?

 Jun 26, 2022
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There are 9 choices for the hundreds digit. 

 

The only possible cases for the tens and units digits are: (0, 5 - 9), (1, 7 - 9), (2, 9)

 

This makes for 9 cases for the units and tens digits. 

 

Thus, there are \(9 \times 9 = \color{brown}\boxed{81}\) cases. 

 Jun 26, 2022

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