Let us assume the total number of balls in the ball pit = x
The total number of red balls in the ball pit = 720
Percentage of red balls among the total balls = 60%
Then
(60/100) * x = 720
3x/5 = 720
3x = 720 * 5
3x = 3600
x = 3600/3
= 1200
So the total number of balls in the pit is 1200.I hope the procedure is clear enough for you to understand. Using this method you can always solve similar problems without taking any help from outside.