Question

How many numbers are less than 1000 that contain only the digits 5 or 6 or both 5 or 6? A digit may be used more than once. 

Answer 1

5,6
55,56
65,66
555,556,565,566
655,656.665.666

Looks like there are 14 numbers that use only the digits 5 or 6 or both 5 or 6 that are under 1000.