The choice when expressing numbers is between using a word to express the number (e.g., three) or a figure (e.g., 3).  Please check whether or not the number is expressed correctly.  Then  highlight the rule that governs the use of the number in this instance.

After studying the passage, the participants had 1 min to complete a set of basic math problems as a distraction task.

The expression of the number is   correct     incorrect       because: