Final answer:
The percentage of a group of students that plays at least one sport is 40%.
Step-by-step explanation:
To determine the percentage of students that play at least one sport, we need to find the complement of the percentage of students that do not play any sports.
Given that two-fifths, or 40%, of the group plays at least one sport, the percentage of students that do not play any sports is 100% - 40% = 60%.
Therefore, the percentage of students that play at least one sport is 100% - 60% = 40%.