What is X% of Y? Multiply Y by X/100. Example: 15% of 200 = 200 × 0.15 = 30.

Percentage increase: ((New − Old) ÷ Old) × 100. Example: 50 to 75 = ((75−50) ÷ 50) × 100 = 50% increase.

X is what % of Y? (X ÷ Y) × 100. Example: 30 is what % of 200? (30 ÷ 200) × 100 = 15%.