standard_description: Identify when two expressions are equivalent (i.e., when the two expressions name the same number regardless of which value is substituted into them). For example, the expressions y + y + y and 3y are equivalent because they name the same number regardless of which number y stands for.
problem_activity: Problem 1
Quiana measures the width of her doorway entrance using a measuring tape. She measures the width as 33 inches. She later finds a better tape measure that measures to the nearest half of an inch. After re-measuring, she determines that the actual measure of the doorway is 32 ½ inches.
a.   What is the amount of error from using the first measuring tape?
b.   What is the error as a percentage of the actual width?
Problem 2
Paul and Kimberly both estimate the weight of their dogs before bringing them to the vet. The table below shows each of their estimates along with the actual weights of the dogs from the vet’s office.
|                | **           Estimate (lbs.)          ** | **           Actual (lbs.)          ** |
|----------------|------------------------------------------|----------------------------------------|
|   Paul's dog   |                    10                    |                  11.5                  |
| Kimberly's dog |                    84                    |                  82.5                  |
Paul notices that both his and Kimberly’s estimates were only 1.5 pounds off from the actual weights. Paul says that means his estimate was as good as Kimberly’s estimate.
Do you agree with Paul? Find the percent error for each person’s guess of their dog’s weight, and use it in your answer.
Problem 3
In science class, Justine measured a rock sample and found it to be 15 grams. Her teacher told her that the scale is off and the actual weight is 0.3 grams more than her measurement.
What is the percent error? Give your answer to the nearest percent.


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