Write the largest and the smallest 7-digit number and also find how many 7-digit numbers are there in all.

Answer

### Step-by-Step Solution

1. **Identify the Largest 7-Digit Number**:
- The largest single-digit number is 9. To form the largest 7-digit number, we fill all 7 places with the digit 9.
- Therefore, the largest 7-digit number is **9,999,999**.

2. **Identify the Smallest 7-Digit Number**:
- The smallest 7-digit number must start with 1 (since a 7-digit number cannot start with 0) followed by six 0s.
- Therefore, the smallest 7-digit number is **1,000,000**.

3. **Calculate the Total Number of 7-Digit Numbers**:
- To find the total number of 7-digit numbers, we subtract the smallest 7-digit number from the largest 7-digit number and then add 1 (to include both endpoints).
- Calculation:
- Largest 7-digit number: 9,999,999
- Smallest 7-digit number: 1,000,000
- Total 7-digit numbers = (9,999,999 - 1,000,000) + 1
- Total 7-digit numbers = 8,999,999 + 1 = 9,000,000.

### Final Answers:
- Largest 7-digit number: **9,999,999**
- Smallest 7-digit number: **1,000,000**
- Total number of 7-digit numbers: **9,000,000**