Download Lesson 5-7

Lesson 5-7
Example 1 Subtract Mixed Numbers
7
1
Find 68 − 48.
Estimate 7 − 4 = 3
Subtract the fractions.
Subtract the whole numbers.
7
68
→
68
1
→
− 48
− 48
7
1
6
8
6
3
28 or 24
Check for Reasonableness
3
24 ≈ 3 
Example 2 Add Mixed Numbers
2
1
Find 43 + 38.
2
Estimate 5 + 3 = 8
1
The LCD of 3 and 8 is 24.
Write the
problem.
Rename the fractions
using the LCD, 24.
43
2
→
2×8
3×8
→
1
→
1×3
8×3
→ + 324
+ 38
Add the fractions. Then
add the whole numbers.
424
16
→
424
16
3
→
+ 324
3
19
724
Check for Reasonableness
19
724 ≈ 8 
Example 3 Real-World Example
1
1
On her daily walk, Sylvia walks 18 miles to the grocery store and then 24 miles to
the post office. Find the distance she walks from her home to the grocery store and
then to the post office.
First use the LCD to rename the fractions. Then add.
1
1
1
2
18 + 24 = 18 + 28
3
= 38
3
Sylvia walks 38 miles from her home to the post office each day.
Example 4 Evaluate an Expression
3
1
ALGEBRA Evaluate d – e if d = 54 and e = 23.
3
1
3
d – e = 5 4 − 23
9
1
Replace d with 54 and e with 23.
4
= 512 − 212
5
= 312
3
9
1
4
Rename 54 as 512 and 23 as 212.
Subtract.
Example 5 Evaluate an Expression
3
7
3
7
ALGEBRA Evaluate m + n if m = 35 and n = 610.
3
7
m + n = 35 + 610
6
7
= 310 + 610
13
= 910
3
3
3
6
Rename 35 as 310.
Add.
= 9 +110
= 1010
Replace m with 35 and n with 610.
13
Write 10 as a mixed number.
Simplify.