Question

How many integers between 1000 and 1999 have three same digits? A. 34 B. 42 C. 72 D. 12

Answer 1

See a solution process below:

Explanation:

First, there are ? solutions of repeating the integers from 2 through 8:

1: 1222
2: 1333
3: 1444
4: 1555
5: 1666
6: 1777
7: 1888

Then we can use different combinations of `1`

8: 1110
9: 1101
10: 1011

Finally, if we include the end points:

11: 1000 has three 0's
12: 1999 has three 9's

The answer is: D. 12