adding fractions: traditional approach
DESCRIPTION
This slide show covers adding two fractions with the same denominator, adding two fractions with one denominator that is a factor of the other, and, finally adding fractions with different denominators. There are a small number of questions for a class to complete as a 'check on learning' during the presentation. I'm assuming the class have access to a textbook or other collection of problems for use after the presentation. This slideshare version is pretty dry. I usually include a visual 'starter' image of some kind, often a funny sign or joke or screen grab of a news article.TRANSCRIPT
Adding Fractions
+
+ =
+ =
+ =
4
3
+ =
4
3+
+ =
4
3
4
1+
+ =
4
3
4
1+ =
+ =
4
3
4
1+ =
4
4
+ =
4
3
4
1+ =
4
41
Same denominators: add the numerators!
+
+ =
+ =
+ =
+ =
8
5
+ =
8
5+
+ =
8
5
8
2+
+ =
8
5
8
2+ =
+ =
8
5
8
2+ =
8
7
+ =
8
5
8
2+ =
8
7
+ =
8
5
4
1+ =
8
7
If the denominators are different, find equivalent fractions, then add numerators
+
+12
5+3
1
+12
5+3
1
+
+
12
5+3
1
+
+
12
5+3
1
+
+
12
5+3
1
+
+
12
5+3
1
12
5
+
+
12
5+3
1
12
5+
+
+
12
5+3
1
12
5+12
4
12
5+12
4
12
5+12
4=
12
5+12
4
12
9=
12
5+12
4
12
9= =
12
5+12
4
12
9= =
4
3
1. Check denominators
1. Check denominators
2. Find equivalent fractions so denominators same
1. Check denominators
2. Find equivalent fractions so denominators same
3. Add numerators
1. Check denominators
2. Find equivalent fractions so denominators same
3. Add numerators
4. Cancel down if needed
1. Check denominators2. Find equivalent fractions so
denominators same3. Add numerators4. Cancel down if needed5. Pull out the whole numbers
if needed
Your turn…
10
3
5
2
4
3
8
7
10
7
10
3
10
4
10
3
5
2
4
3
8
7
10
7
10
3
10
4
10
3
5
2
8
51
8
13
8
6
8
7
4
3
8
7
Sometimes, you have to change both denominators…
5
4
4
3
5
4
4
3
5
4
4
3
You need a number that is a multiple of both 4 and 5…
5
4
4
3 =
20
?
20
?
5
4
4
3 =
20
?
20
?
=20
16
20
15
5
4
4
3 =
20
?
20
?
=20
16
20
15 =
20
31
5
4
4
3 =
20
?
20
?
=20
16
20
15 =
20
31=20
111
1. Check denominators
1. Check denominators
2. Find ‘common denominator’ (LCM)
1. Check denominators
2. Find ‘common denominator’ (LCM)
3. Add numerators
1. Check denominators
2. Find ‘common denominator’ (LCM)
3. Add numerators
4. Cancel down if needed
1. Check denominators2. Find ‘common
denominator’ (LCM)3. Add numerators4. Cancel down if needed5. Pull out the whole numbers
if needed
Your turn…
4
3
6
1
3
2
4
1
12
11
12
8
12
3
3
2
4
1
4
3
6
1
12
11
12
9
12
2
4
3
6
1
12
11
12
8
12
3
3
2
4
1
Sometimes, you have to add fractions larger than one…
3
21
2
12
I suggest making these fractions ‘top heavy’.
3
11
2
12
3
11
2
12 =
3
4
2
5
3
11
2
12 =
3
4
2
5
6
8
6
10=
3
11
2
12 =
3
4
2
5
6
8
6
10=
= 6
18
3
11
2
12 =
3
4
2
5
6
8
6
10=
= 6
18= 3
Now find an exercise in the book or a work-sheet and practice!