How many 7's are there in the numbers from 1 to 999,999?

For example 17 has one 7 and 3707 has two. How many are there altogether? I could have said from 1 to 1,000,000. Think of the choice of 999,999 as a hint of sorts. Knowledge of combinatorics may get in the way. There is a complicated combinatoric, solution but a very simple one making use of symmetry, provided that you see the problem in the right way. You should be able to do the arithmetic in your head. After finding the number of 7’s, find the number of 0’s. It takes just a little bit more of work. If you are good at mental math, you could also do the arithmetic for the 0 count in your head.