Number Sense

Percent problems without panic

Percent of a number = (percent ÷ 100) × number.

Three forms

X% of Y is what? → (X/100)·Y. What % of Y is Z? → (Z/Y)·100. X% of what is Y? → Y/(X/100).

20% off = pay 80%. 15% tax = pay 115%. Multiply by the new percent (0.80 or 1.15) in one step instead of computing the discount and subtracting.

20% off then 10% off is NOT 30% off. It's 0.80 × 0.90 = 0.72, so 28% off. Apply percentages in sequence, never add them.

Tip: revisit this strategy after every 10 missed questions on this topic.