He's using the graduated cylinder method. I think the volume might be between 15 and 20. (It's kind of not obvious...)
135+124+140+122+409+132+119+128+136+125=1570
1570/10= 157 customers at average
The percent discount was,
55.5556. It could be changed to 56%, but as a whole it would more than likely be 55%.
-Mabel <3
The formula is Opposite/Hypotenuse
82/100 or 41/50 if you simplify
