Unit 6, Lesson 4
Increasing and Decreasing
Accelerated 6
Preparation
Lesson Narrative
In this lesson, students make sense of situations involving percent increase and percent decrease, where a change is expressed as a percentage of the original amount. They use tape diagrams to represent the situations, and they calculate the new amount. This builds on students’ previous work with situations where an increase or decrease is expressed as a fraction or decimal part of the original amount.
Students make sense of problems involving percent increase as they consider various strategies and representations to persevere in solving (MP1). As students use tape diagrams to make sense of the relationships between the quantities, they are making use of structure (MP7).
- Coordinate statements about “percent increase” or “percent decrease” with comparisons to the original amount, e.g., a 20% increase means the new value is 120% of the original value.
- Draw and label a tape diagram to represent a situation that involves adding or subtracting a percentage of the initial value.
- Explain (orally and in writing) how to calculate the new amount given the original amount and a percentage of increase or decrease.
Let’s use percentages to describe increases and decreases.
Required Preparation
None
A percent decrease tells how much a quantity went down. It is written as a percentage of the starting amount.
For example, a store had 64 hats on Friday. It had 48 hats left on Saturday. The number of hats went down by 16.
This was a 25% decrease, because 16 is 25% of 64.
A percent increase tells how much a quantity went up. It is written as a percentage of the starting amount.
For example, Elena had \$50 in the bank on Monday. She had \$56 on Tuesday. The amount went up by \$6.
This was a 12% increase, because 6 is 12% of 50.