Task 1. The houses on a street are numbered from 1 to 100. How many times does the digit 7 appear in the house numbers? List all such numbers.
Solution. The numbers from 1 to 100 that have a seven in their representation are $7, 17, 27, 37, 47, 57, 67, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 87,$ and 97. Therefore, the digit 7 appears a total of 20 times.