If the observed prevailing visibility is 4 1/4sm, what visibility would be reported on the MF1M-10C?

The prevailing visibility reported in aviation weather is typically rounded to the nearest whole statute mile for simplicity and standardization in reporting. In this case, with an observed prevailing visibility of 4 1/4 statute miles (4.25), the convention is to round down to the nearest whole number when visibility is less than five miles. Therefore, the reported visibility would be rounded to 4 statute miles.

This rounding practice is particularly important in aviation to ensure clarity and consistency in communication among pilots and air traffic controllers, as well as in weather reporting systems like the MF1M-10C. The other options do not adhere to this rounding convention, making the 4 statute miles the most appropriate and standard report.