There are 18 two-digit numbers that contain the digit 7.
Understanding the Solution
We can approach this problem by considering the possible positions of the digit 7 within a two-digit number. The digit 7 can appear in either the tens place or the units place (or both).
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7 in the units place: If 7 is in the units place, the tens place can be any digit from 1 to 9. This gives us 9 possibilities (17, 27, 37, 47, 57, 67, 77, 87, 97).
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7 in the tens place: If 7 is in the tens place, the units place can be any digit from 0 to 9. This gives us 10 possibilities (70, 71, 72, 73, 74, 75, 76, 77, 78, 79).
Adding these possibilities together, we have 9 + 10 = 19 numbers. However, we've double-counted the number 77. Therefore, the total number of two-digit numbers containing the digit 7 is 19 - 1 = 18.
Examples
Here are some examples of two-digit numbers containing the digit 7:
- 17
- 27
- 70
- 77
- 87
- 97
The provided references consistently confirm that there are 18 two-digit numbers containing the digit 7.
