Transcript 7-8 Work Problemsx

7-8 Work Problems
Objective: To solve work problems
7-8 Work Problems
Use the formula:
 Work Rate X time = work done
rt=w
Work rate means the fractional part
of a job done in a given unit of
time.

7-8 Work Problems
Example 1:
Sheri can rake the lawn in 2 h. Her
work rate is the part of the job she
can do in 1 h.
 r t = w r = w/t r = 1/2
Therefore  her work is ½ job per
hour.
7-8 Work Problems
 Example 2:
 Josh can split a cord of wood in 4 days.
 His father can split a cord in 2 days.
 How long will it take to split a cord of
wood if they work together.
7-8 Work Problems
 Example 2:
 Josh can split a cord of wood in 4 days.
 His father can split a cord in 2 days.
 How long will it take to split a cord of wood if they work together.
 Step 1: Find the number of days the job
will take them.
 Step 2: Let x = number of days needed
 Step 3: Since josh does the job in 4
days: his work rate = ¼.
7-8 Work Problems
 Example 2:
 Josh can split a cord of wood in 4 days.
 His father can split a cord in 2 days.
 How long will it take to split a cord of wood if they work together.
 Step 3: Since his father does the job in
2 days his work rate =1/2.
Work rate X Time
Josh
Father
1/4
1/2
X
x
= Work
done 
7-8 Work Problems
 Example 2:
Work rate X Time
Josh
Father
1/4
1/2
= Work
done 
X
x
 Step 3: Josh’s part + Father’s Job is whole job.
 Step 4: Solve 
7-8 Work Problems
 Example 3: Robot A takes 6 min to weld a fender. Robot
B takes only 5 ½ min. If they work together for 2 min.
How long will it take Robot B to finish welding the
fender by itself.
 X = number of minutes needed for Robot B to finish.
 Robot B’s work rate =
1

5 1/2
Work rate X Time
Robot A

Robot B
1/6
2/11
2
2+x
= Work
done 
7-8 Work Problems
 Example 3:
Work rate X Time

Robot A
Robot B
1/6
2/11
= Work
done 
2
2+x
 A’s part of job + B’s part = whole job
7-8 Work Problems
 Homework: P. 328 1 – 15 odds