Unit 3: Fractions
Section 9: Adding and subtracting fractions
Goals:
- Recognize word problems that include multiplication
- Write word problems for addition
- Write word problems for subtraction.
- Add and subtract with materials
- Add and subtract with square or rectangle diagrams
- Add and subtract with least common denominators
Warning! This week looks
short. It does have less different stuff in it than last
week's assignments did. It is an illusion that this is
easier. It's not. This topic usually takes a full
week, because, after doing all this in 1-2 days, students in an
in-person will turn in assignments, and I will discover they have
missed half of the important ideas. Then I have to stop the
class and redo everything, and make everyone in the class redo
everything. I will do that to you, if you miss stuff the
first time around. Watch and read carefully, think about
details, and don't get lulled into a false sense of security
because it seems easy.
Writing word problems
Adding and subtracting with materials:
Watch: Examples of how to explain
adding and subtracting fractions with different denominators
Assignment:
Adding and subtracting with array pictures or materials
Read: My
written example of how to explain
adding fractions with different denominators
Assignment:
Assn 49: Record (video) a
detailed description of how to add fractions using an array
diagram, paying special attention to how the array is formed,
and how the equivalent fractions are deduced using
multiplication from the array (3/8 + 4/5).
I recommend that you wait
until you have feedback on this addition explanation, before
doing Assn 50. Email me to get feedback right away.
Assn
50: Then, do the same thing for a subtraction of fractions
problem (7/8 - 2/3).
Instructions for
explanation
videos about fractions
Adding and subtracting fractions numerically:
with and without a least common denominator
Watch: 3 levels of abstraction in
numerical fraction work
Assignment:
Assn 51: Choose
a fraction addition or subtraction problem where:
- the least common denominator is smaller than the denominator
that you get by multiplying the two denominators (so you if
you multiplied the denominators to find a common denominator,
you would need to simplify at the end),
- neither denominator is a multiple of the other (for example,
6 is a multiple of 2, so you can't use halves and sixths)
Show how compute the sum or difference in all 3 ways I showed.
(Pencil and paper work is sufficient--carefully show all steps
in your work).