Mr. Sato needs 9 magnets.
Explanation:AS there are 24 students in the science class,
there are 242=12 pair of students.
Mr. Sato wants to give each pair of students 3 magnets
Mr. Sato has already given 9 pairs of students their 3 magnets
Therefore number of pairs of students yet to be given magnets is 12−9=3.
For them he needs 3×3=9 magnets.