Worked examples
Two examples
Example 1
A plumber’s bill is $150 for 2 hours and $285 for 5 hours. How much does each extra hour add?
- Change in cost over change in hours: (285 − 150) ÷ (5 − 2) = 135 ÷ 3.
Answer: $45 per hour
Example 2
A tank holds 80 gallons at noon and 50 gallons 6 hours later, draining steadily. What is the slope?
- (50 − 80) ÷ 6 = −30 ÷ 6.
- Negative, because the water goes down.
Answer: −5 gallons per hour
Where this is taught: Quiz 42: Lines, Slope, and Systems, “Slope is a rate”
The drill
Ten problems
This drill also has challenge problems. They use the same skill, set up the way the GED test sometimes sets up a problem, so that it looks new at first.
How many:
Type the number only; the unit is already there. Then press Check my answers at the bottom.Write each answer on the line. The answer key, with the reasoning, is on the last page.