Percent and percent change
Percent is a ratio with denominator 100, so p% of a quantity is p/100 times it. Students find a percent of a number, find the whole from a part and a percent, and handle increase, decrease, tax, discount, and markup. Percent change is measured against the original amount unless the problem says otherwise. Two things to show with a bar: increasing 80 by 25% is not 80 + 25, and decreasing by 20% then increasing by 20% does not return to the start (it lands at 96%). Reverse-percent problems (the sale price is known, find the original) appear at a basic level here and in full in Math 7.
Specification · for a parent or teacher
- percent-change
- Advanced Math 6 · Unit 7
- High School Math 1
- Applied
- 3 of 4 — Grade 6–7 core. Multi-step, first symbolic work.
- 5 items
Students can
; percent of a quantity; whole given a part and a percent; increase, decrease, tax, discount, markup.
Ready when
they can show that −20% then +20% is not identity, with a bar.
Formulas
Watch for
increase 80 by 25% as 80 + 25; decrease 80 by 25% then increase by 25% and expect 80 back.