Today’s Date:

11/15/11

“Work” Word Problems

Notes on Handout

“Work” Equation

Together + Together = 1

Alone Alone

Always “together Over alone + together Over alone”

Always equals 1

Ex 1) Nora needs 3 hours to chop down the tree in front of her house. Her younger brother needs 6 hours to do the same job.

How much time would it take them if they worked together?

Nora’s Part of Job

Bro’s Part of Job

1 Whole Job Completed

+ =

3

x

6

x 1

2 6x x

(2) (1)(6)

Multiply every term to get the common denominator

3 6x 2x

Example 1 cont…

a) Define variable:

b) Write the equation:

c) Solve:

13 6

x x

x is time together

2 hours (to complete the job together)

T.O.O. SET-UP #3

Do NOT finish the problem.This time they give Sean’s time & time together, but not Ian’s time.

3.5 3.51

6 x

Example 2 (#4 on WS)

An inlet pipe can fill a tank in 3 hours. It takes 11 hours for the drainpipe to empty the tank. How long will it take to fill the tank if both the inlet pipe and the drainpipe are open?

=Inlet and Drain pipe are working against each other.So, make Drain pipe’s rate alone negative.

3

x

11

x 1

Example 2 cont…

13 11

x x

11 3 33

8 33

4.125 hours

x x

x

x

(11) (3)(33)

Example 3 (#5 on WS)

Crane A can unload the container ship in 10 hours, and crane B can unload it in 14 hours. Crane A started to unload the ship at noon and was joined by crane B at 2 pm. At what time was the unloading job of the ship completed?

Crane A: Started at noon (12:00)Crane B: Started at 2:00 Let x = Crane B’s timeCrane A worked 2 hours more than Crane B : x + 2

Example 3 cont…

21

10 14

x x

Once you get x, you need to add that time to 2:00 to get “WHAT TIME” job was finished.

Finish for HW. Your answer will be a decimal so round to the nearest tenth and convert to “Time”

T.O.O.

Work with a neighbor to set up #6.Do NOT finish the problem.

Clue: Larger Pump’s time is x – 7

12 121

7x x

Homework

#8 Finish “Work” Problems side of WS

a) Define Variable

b) Write equation

c) Solve

Products & Quotients; Sums & Differences side: do Every Other Odd

(1, 5, 9, 13, 17, 21)