Midday Check

“The Mississippi River drains about forty percent of the contiguous United States.”

Bayline Desk

This one matches the record. The U.S. Geological Survey describes the Mississippi River watershed as about 1.2 million square miles, roughly forty percent of the contiguous United States. A broadcast can round a figure and still be faithful when the primary source rounds it the same way. Nothing left out of the sentence changes what it means.