Cogito
Grade 4 Math · Chapter 5 · Lesson 3
Comparing Unlike Fractions
Make the pieces the same, then count.
10 problems · about 16 minutes · 4.NF.A.2
What this lesson teaches
The child compares two fractions with different numerators and denominators.
- Rewrite both fractions in the same unit, then count.
- Comparing to a half is often quicker.
- Both fractions must be of the same whole.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Equivalent Fractions: 2/3 = ?/9. What is the top number?
Answer 6
Why 2/3 = 6/9.
Review — A Fraction Counts Units: How many sixths are in 5/6?
Answer 5
Why 5/6 is 5 copies of 1/6.
Warm Up
Straightforward practice. Get the method working first.
4 problems2/3 written in twelfths has what top number?
Answer 8
Why 2/3 = 8/12.
Why can you not compare 2/5 and 1/2 by counting?
Answer The pieces are different sizes.
Why Counting only works when the units match.
Is 3/4 bigger than 2/3?
Answer Yes. 9/12 beats 8/12.
Why Use twelfths.
3/5 written in tenths has what top number?
Answer 6
Why Both numbers double.
Build It Up
The same ideas with more to keep track of.
2 problemsIs 4/9 more or less than a half?
Answer Less.
Why Half of 9 is 4.5.
Is 5/6 bigger than 7/12?
Answer Yes. 10/12 beats 7/12.
Why Use twelfths.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Two Jugs: One jug is 5/8 full, another 1/2. Which has more?
Answer 5/8.
Why 5/8 is more than 4/8.
The Reading: Ana read 2/5 of her book, Leo 3/8 of his. Who read more, if the books are the same?
Answer Ana.
Why 2/5 = 16/40 and 3/8 = 15/40, so Ana read more.