Cogito
Grade 3 Math · Chapter 5 · Lesson 1
Equal Parts of a Whole
Cutting fairly is where fractions start.
10 problems · about 12 minutes · 3.NF.A.1, 3.G.A.2
What this lesson teaches
The child partitions a shape into equal parts and rejects unequal partitions.
- A fraction needs equal parts.
- The denominator counts those parts.
- More parts always means smaller pieces.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Area of Joined Shapes: A 6 by 3 part and a 4 by 2 part. Total area?
Answer 26
Why 18 + 8 = 26 square units.
Review — Same Area, Different Shape: A 2 by 9 rectangle. What is its area?
Answer 18
Why The area is 18 square units.
Review — Telling Area and Perimeter Apart: A rectangle 9 by 4. What is its area?
Answer 36
Why The area is 36 square units.
Warm Up
Straightforward practice. Get the method working first.
3 problemsA shape cut into 5 equal parts. What is the denominator?
Answer 5
Why The denominator is 5.
What does the denominator tell you?
Answer How many equal parts the whole was cut into.
Why The denominator counts the parts the whole was cut into.
A shape cut into 8 equal parts. What is the denominator?
Answer 8
Why Count the parts.
Build It Up
The same ideas with more to keep track of.
1 problemMust the parts be equal to name a fraction?
Answer Yes. Always.
Why Think about sharing fairly.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsA whole cut into 3 equal parts. What is one part called?
Answer A third.
Why Three equal shares.
The Pizza: A pizza is cut into 6 equal slices. What is the denominator?
Answer 6
Why The denominator is 6.
Smaller Pieces: Which gives smaller pieces, cutting into 4 parts or into 8?
Answer Into 8.
Why More parts always means each part is smaller.