1. What is X% of Y?
To find X% of Y, use the formula:
$(X / 100) \times Y$
**Example:** To find 20% of 150:
$(20 / 100) \times 150 = 0.20 \times 150 = 30$
2. X is what percent of Y?
To find what percentage X is of Y, use the formula:
$(X / Y) \times 100$
**Example:** To find what percentage 30 is of 150:
$(30 / 150) \times 100 = 0.20 \times 100 = 20\%$
3. Percentage Change (Increase/Decrease)
To calculate the percentage change from an old value to a new value, use the formula:
$( (New Value - Old Value) / Old Value ) \times 100$
**Example (Increase):** From 100 to 120:
$((120 - 100) / 100) \times 100 = (20 / 100) \times 100 = 20\%$ Increase
**Example (Decrease):** From 100 to 80:
$((80 - 100) / 100) \times 100 = (-20 / 100) \times 100 = -20\%$ (20% Decrease)