A six-digit odometer in a car shows how many kilometers the car has traveled since it was purchased. Currently, it displays a number that contains four "sevens". Could it be that after another 900 km, the odometer will display a number with exactly one "seven"?
To end up with only one "seven", we need to get rid of the other three. Note that when adding 900 to a six-digit number, the digit in the hundreds place will definitely change. Moreover, if the digit in the hundreds place was not zero, the digit in the thousands place will also change. Thus, we can eliminate two "sevens".

To change another digit in the original number, the digit in the thousands place must be 9. But in this case, we won't get rid of the "seven" because we eliminated the "nine" instead. Therefore, the digit in the ten-thousands place must also be 9. In this case, the original number on the display is 799777. But 799777 + 900 = 800677, which means the sum contains two "sevens".

Therefore, it is impossible to get a number with only one "seven".

## Answer

no, it cannot.