Mathematics · Grades 5–9
Percentages and proportions
A focused reference to use alongside your practice.
Percent of a quantity
Convert the percentage to a fraction or decimal before multiplying.
part = whole × p/100
15% of 80 = 0.15 × 80 = 12
Percentage change
The original value is the reference and must not be zero.
change % = (new − original)/original × 100
40 → 50: (50 − 40)/40 × 100 = 25%
Direct proportion
For a direct proportion, the ratio y/x stays constant for x ≠ 0.
y = kx
3 notebooks → 12 units; 5 notebooks → 20 units
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.