Cogito
Grade 7 Math · Chapter 3 · Lesson 1
Percent Increase and Decrease
Change measured against where you started.
10 problems · about 18 minutes · 7.RP.A.3
What this lesson teaches
The child computes percent increase and decrease and finds the new amount.
- Percent change is the change divided by the original.
- A rise multiplies by more than 1, a fall by less.
- Up 10% then down 10% does not return to the start.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
1 problemReview — Unit Rates with Fractions: ⅖ mile in ⅕ hour. Miles per hour?
Answer 2
Why 2 mph.
Warm Up
Straightforward practice. Get the method working first.
4 problemsA 120 pound item falls 25%. New price?
Answer 90
Why 90 pounds.
Percent change is divided by which amount?
Answer The original amount.
Why Always the original.
A 50 pound item rises 10%. New price?
Answer 55
Why 50 × 1.1.
A 90 pound item falls 20%. New price?
Answer 72
Why 90 × 0.8.
Build It Up
The same ideas with more to keep track of.
2 problemsFrom 20 to 25. Percent increase?
Answer 25
Why 5 ÷ 20.
From 50 to 40. Percent decrease?
Answer 20
Why 10 ÷ 50.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsThe Sale: A 60 pound coat is reduced by 25%. What is the new price?
Answer 45 pounds
Why 45 pounds.
The Rise: A price rises from 80 to 100. What is the percent increase?
Answer 25 percent
Why 25%.
The Tax: A 200 pound item has 20% tax added. What is the total?
Answer 240 pounds
Why 240 pounds.