Page 78 - Math Course 1 (Book 1)

Unlike Fractions

Mo. 2

Lesson 5

Add Fractions and Mixed Numbers
KEY CONCEPTS:
1. Add unlike fractions.
2. Subtract unlike fractions. Examples

(
5 3
Find + - ( Write in simplest form.
6 10
MO. 2 - L5a Estimate: 1 + 0 = 1

Add Unlike Fractions 5 + - 10 ( = 5 5 + - 10 ( 3
3
3
(
(
6
6
5
3
The LCD is 2 • 3 • 5 or 30.
Key Concept = 25 + - 30 (
9
30 (
Rename each fraction with the LCD.
Adding Unlike Fractions
Words To add fractions with unlike denominators, Answer = 16 or 8 Compare to the estimate.
rename the fractions with a common 30 15 Is the answer reasonable?
denominator.
Then add and simplify as with like fractions.
3 (
(
Find 2 1 + -3 2 Write in simplest form.
1 2 1 5 2 3 8
Example 3 + 5 = 3 5 + 5 3
Estimate: 2 + (-4) = -2
5 6 11
= + or
15 15 15
3 (
(
3 (
(
2 1 + -3 2 = 17 + - 11 Write the mixed
8 8 numbers as
improper fractions.
Let’s Begin = 17 3 + - 11 8 Rename fractions
(
3 (
8 3 8 using the LCD, 24.
24 (
(
= 51 + -88 Simplify.
Add Unlike Fractions 24
-37 + -1 13 Compared to the
=
Answer
estimate, the answer
Example 24 24 is reasonable.
3 1
Find +
4 7
3 + 1 = 3 • 7 + 1 4 Use 4 • 7 or 28 as the
4 7 4 7 7 4 common denominator.

21 4 Rename each fraction with
= +
28 28 the common denominator.
25
Answer = Add the numerators.
28

70