The difference between two values divided by the average of the two values. Shown as a percentage.
Difference means to subtract one value from another (such as Alex sold 15 tickets, and Sam sold 25; the difference between 25 and 15 is: 25-15 = 10)
Average is the value half-way between:
(first value + second value)/2
The average of 25 and 15 is: (25+15)/2 = 40/2 = 20
The DIFFERENCE as a percentage is:
Difference is 25-15 = 10
Average is (25+15)/2 = 20
10 as a percentage of 20 is:
(10/20) * 100 = 100/2 = 50%