Math 7 · Unit 2, Lesson 6
More Than One Change
Tax, then tip, one step at a time.
I say it the way your test says it.
And I say it the way you would say it to a friend. Same idea, two ways.
Write it down. Do every step on paper, one line per step. Percent problems go wrong in your head, not on the page. If you changed something, it should be on the paper.
Go in order. Each tile has a short explanation, then a "Let me try a few" button.
When you have finished
At the end of each tile you will find a review form to give us feedback.
NC standards: NC.7.RP.3, NC.7.EE.3.
Words we use
| Word | Plain English | What you do |
|---|---|---|
| Subtotal | The total before tax or tip. | Find it first; the percents are taken from it. |
| One step at a time | Finish one change before starting the next. | Write each line, then apply the next percent to that line. |
| Percent of what | The whole the percent is taken from. | Ask it at every step; it changes after each one. |
| Discount, tax, tip, commission | From Lessons 3 and 4. | Each one is a multiplier, applied in order. |
The big idea
A proportional relationship always multiplies by the same number, the unit rate.
Percent means out of 100. A percent is a unit rate for 100 instead of for 1: 30 percent means 30 for every 100.
This lesson added problems with more than one percent. Finish one change before you start the next, and at every step ask percent of what, because the whole changes after each one. Each percent change is one multiplier, and you apply them in order. That is why percents do not add: up 10 percent then down 10 percent lands at 99, and 20 percent off then 10 percent off is 28 percent off, not 30.
Exit ticket
On paper or an index card. Use the math word and the plain-English word.
- A $50 jacket is 20 percent off, and then 6 percent tax is added. What do you pay?
- A $100 jacket goes up 10 percent, then down 10 percent. Where does it land?
- Why are two 10 percent discounts not a 20 percent discount?
Check your exit ticket
- $42.40.
- $99.
- The second 10 percent is taken from a smaller number than the first.
Printables
A one-page study guide with Elle and Finn, the two big-idea sentences, the one-step-at-a-time rule, the used car, and the surprise. Plus a worksheet with an answer key and a lesson plan that walks a parent or tutor through the three tiles.
Where this goes next
NC Grade 7 standards in this lesson: NC.7.RP.3, NC.7.EE.3.