Cogito
Grade 3 Math · Chapter 5 · Lesson 2
Unit Fractions
One piece out of the whole.
10 problems · about 12 minutes · 3.NF.A.1
What this lesson teaches
The child identifies a unit fraction as one part of a whole split into b equal parts.
- A unit fraction has 1 on top: one single piece.
- The numerator counts the parts you have.
- A bigger denominator makes a smaller piece.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Equal Parts of a Whole: A shape cut into 5 equal parts. What is the denominator?
Answer 5
Why The denominator is 5.
Review — 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.
Warm Up
Straightforward practice. Get the method working first.
3 problemsWhich is bigger, 1/4 or 1/6?
Answer 1/4
Why 1/4 is bigger, even though 4 is the smaller number.
What does the numerator tell you?
Answer How many parts you have.
Why The numerator counts the parts you have.
Which is bigger, 1/3 or 1/5?
Answer 1/3
Why Fewer parts, bigger pieces.
Build It Up
The same ideas with more to keep track of.
1 problemWhich is bigger, 1/6 or 1/2?
Answer 1/2
Why A half is a big piece.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsHow many eighths make one whole?
Answer 8
Why All the pieces.
Sharing a Cake: Would you rather have 1/3 of a cake or 1/6 of the same cake?
Answer 1/3.
Why 1/3 is a bigger piece than 1/6.
The Smallest Piece: Which is the smallest: 1/2, 1/5, or 1/8?
Answer 1/8.
Why 1/8 is the smallest, because the whole was cut into the most parts.