The key is to move 1 marble from 1 corner to a side. For example, move 1 marble from pile A to pile B. The bottom side of the triangle only has 8 marbles left. Add 1 marble to pile C, all 3 sides still have 9 marbles.

Free challenging math problems for Kids (1st grade, 2nd grade, 3rd grade, 4th grade, 5th grade, 6 grade and 7th grade)