Browse · MATH
Printjmc
prealgebra senior
Problem
How many integers between 100 and 500 have at least two 3s as digits?
Solution
First consider the two s to appear in the units and tens places. Between and , there are four such numbers: , , , and . Now consider the two s to appear in the units and hundreds places. The numbers will be in the s, so we don't need to worry about if they are between and . There are choices for the tens digit, but we have already counted , so such a scenario will add nine numbers. Finally, consider the two s to appear in the tens and hundreds places. Again, these numbers are automatically between and . There are choices for the units digit, but we again discard for a final count of nine such numbers. Thus, our answer is .
Final answer
22