Percentage, profit & loss

Percentage

x% of y = x × y / 100

x% of y = y% of x

Percentage change

Change % = (New − Old) / Old × 100

Successive change

Net % = a + b + ab/100

Use −a for a decrease

Profit %

Profit % = (SP − CP) / CP × 100

Profit and loss are always on CP

Selling price

SP = CP × (100 + P%) / 100

Discount

SP = MP × (100 − D%) / 100

Discount is on marked price

Successive discounts

Single discount = a + b − ab/100

Same SP, x% gain and x% loss

Net loss % = x² / 100

Always a loss

Price rise, keep spend same

Cut in consumption % = r / (100 + r) × 100

r = % rise in price

False weight gain

Gain % = Error / (True − Error) × 100