How many of the natural numbers from 1 to 600, inclusive, contain the digit 5 at least once or the digit 6 at least once?
+236 Use complementary counting and count the number of integers that don't contain 5 OR 6 and subtract it from the total numbers.
Ways to pick the first digit: 4. Possible ways: 1, 2, 3, 4
Second digit: 8 because you can't have 5 or 6
Third digit: 8 same as the second
4*8*8=256
Total numbers: 600
600-256=344
:D
