Work problems

• #22:An experienced bricklayer constructs a small wall in 3 hours. The apprentice (you) completes the job in 6 hours. Find how long it takes if they work together.The answer is not 4.5 hours (no averaging!)The answer is not 9 hours (Makes no sense!!)

An experienced bricklayer constructs a small wall in 3 hours. The apprentice (you) completes the job in 6 hours.

Find how long it takes if they work together.

Make a chart!

Equation set-up:1/3 + 1/6 = 1/x

Solution: x = 2 hrs

Hours to complete total job

Part of job completed in 1 hr

Experienced worker 3 1/3

You 6 1/6

Team effort x 1/x

#21 Section 5.6• Smith Engineering found that an experienced surveyor surveys a

roadbed in 4 hours. An apprentice surveyor needs 5 hours to do the job. If the two work together, find how long it takes them to complete the job?

• Set-up: LCD = 20x• 1/4 + 1/5 = 1/x Solution x = 20/9 hours

How long to finish the job

Portion of the job completed in 1 hr.

Co-worker 4 hrs ¼

Apprentice 5 hrs 1/5

Team or working together

X 1/x

#26: Distance = Rate X Time

• A boat can travel 9 miles upstream in the same amount of time it takes to travel 11 miles downstream. If the current of the river is 3 mi/hr, complete the chart below and use it to find the speed of the boat in still water.

A boat can travel 9 miles upstream in the same amount of time it takes to travel 11 miles downstream. If the current of the river is 3 mi/hr, complete the chart below and

use it to find the speed of the boat in still water (let boat speed = x).Dist = rate x time time = Dist/rate

Distance Rate (boat & river) Time

Upstream (against river current – slows you down)

9 mi X - 3 (Same time)

Downstream (with river current – speeds you up)

11 mi X + 3 (Same time)

Set-up:

9(x+3) = 11 (x-3)9x+27 = 11x-3327+33 = 11x – 9x60 = 2x30 = x

The speed of the boat in still water is 30 mi/hr

9 11

3 3x x