there are balls between 20 and 40, when Max counts them by 5's there is one left, when he counts it by three he finds 2 balls left, what's the exact number of balls in the box?.

So because the range is between 20 and 40, it can be noticed through counting.

5, 10, 15, 20, 25, 30, 35, 40

3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39

The number of balls in the box, just from the information by 5, is either ending in 1 (for example 21, 31) or 6 (26, 36)

From counting by 3 with that information, it would mean the number is most likely 26 balls, since there would be one left when Max reaches 25 counting by 5, and two left when he reaches 24 counting by 3.

practice. practice. practice.