Question

Tom was asked to paint the number of plates on 100 apartments which means he will have to paint numbers 1 through 100. Can you figure out the number of times he will have to paint the number 8?

Answer 1

Well, the easy way to do this is to just list every number between 1 and 100 that has a seven in it and then count the sevens:

7, 17, 27, 37, 47, 57, 67, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 87, and 97.

Now, this is a bit of a trick question because at first you just think to start at 7 and every 10 numbers afterward there’s another 7, so there must be 10 sevens, but the trick is when you get into the 70’s, all of them have a leading 7 digit so you have to count them all, and 77 has two sevens in it. Counting all of the sevens should give you 20 sevens total.