How the percentage formulas work
What is X% of Y?
X ÷ 100 × Y
15% of 240 is 0.15 × 240 = 36.
X is what percent of Y?
X ÷ Y × 100
36 out of 240 is 36 ÷ 240 × 100 = 15%.
Percentage increase or decrease
(New − Old) ÷ Old × 100
Sales falling from 1,250 cases to 1,085 is (1,085 − 1,250) ÷ 1,250 × 100 = a 13.2% decrease.