How many times does the digit '7' appear in the numbers from 1 to 100 (inclusive)?
Correct: 20
Let's count the occurrences of the digit '7':
1. **Numbers where '7' appears in the units place:**
7, 17, 27, 37, 47, 57, 67, 77, 87, 97. (This accounts for 10 occurrences of '7')
2. **Numbers where '7' appears in the tens place:**
70, 71, 72, 73, 74, 75, 76, 77, 78, 79. (This accounts for 10 occurrences of '7')
If we sum these counts, we get 10 (from units place) + 10 (from tens place) = 20.
The number '77' is crucial here: it contains the digit '7' twice. When we listed '77' in the units place group, we counted one '7'. When we listed '77' in the tens place group, we counted the *other* '7'. Therefore, by simply adding the counts from the units and tens places, we are correctly accounting for both '7's in '77'.
So, the digit '7' appears a total of 20 times.