Our math book has 15 1 pages, and the page number of each page consists of 10 numbers from 0 to 9. How many figures were used?
1 to 9, which is nine.
10 to 99, that is, (99-10+1) × 2 =180.
From 100 to 15 1, it is (151-100+1) × 3 =156.
So a ***9+ 180+ 156=345.