To find a percentage of a number: multiply the number by the percentage, then divide by 100
To convert a percentage to a decimal: divide by 100
To convert a decimal to a percentage: multiply by 100
To find what percent one number is of another: divide the part by the whole, then multiply by 100
To increase a number by a percentage: multiply by 1 plus the percentage as a decimal
To decrease a number by a percentage: multiply by 1 minus the percentage as a decimal
To find the original number after a percentage increase: divide by 1 plus the percentage as a decimal
To find the original number after a percentage decrease: divide by 1 minus the percentage as a decimal
To find the percentage change: subtract the old value from the new value, divide by the old value, then multiply by 100
To find a discount amount: multiply the original price by the discount percentage, then divide by 100
To find a final price after discount: subtract the discount amount from the original price
To find tax amount: multiply the price by the tax percentage, then divide by 100
To find final price after tax: add the tax amount to the original price
To find a tip amount: multiply the bill by the tip percentage, then divide by 100
To find the total with tip: add the tip amount to the bill
To find a percentage point difference: subtract one percentage from another
To compare percentages: use the same base value before calculating
To estimate quickly: use 10%, 5%, and 1% as shortcuts
To check your answer: make sure the percentage result is reasonable for the numbers used