standard_description: Understand that rewriting an expression in different forms in a problem context can shed light on the problem and how the quantities in it are related. For example, a + 0.05a = 1.05a means that “increase by 5%” is the same as “multiply by 1.05.”
problem_activity: Problem 1
For Simon’s birthday, he and his family go out to eat at a restaurant.
a.   The amount of tax is $3.40, which is 5% of the food bill. How much was the food bill not including the tax?
b.   If Simon wants to leave a 20% tip on the amount of the food bill before tax, how much should he leave for a tip?
c.   What is Simon’s total bill including tax and tip? What percent of the food bill is this?
Problem 2
Emily has a coupon for 20 percent off of her purchase at the store. She finds a backpack that she likes on the discount rack. Its original price is $60, but everything on the rack comes with a 30 percent discount.
Emily says, “
Thirty percent and twenty percent make fifty percent, so it will cost $30.
”
Is Emily correct? Explain your reasoning. In your explanation, if you disagree with Emily, find the price she will pay for the backpack.
Problem 3
In order to make money, a store marks up its prices by 25% from the warehouse prices. Let
$$p$$
represent the price at which the store gets its merchandise from the warehouse, and let
$$s$$
represent the price the store sells the merchandise for after the markup.
a.   Write an equation to determine the selling price,
$$s$$
, based on the warehouse purchase price,
$$p$$
.
b.   Create a table showing possible pairs of solutions to the equation.
| **                Warehouse price (                                 $$p$$                                )               ** | **                Selling price (                                 $$s$$                                )               ** |
|-----------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------|
|                                                                                                                             |                                                                                                                           |
|                                                                                                                             |                                                                                                                           |
|                                                                                                                             |                                                                                                                           |
|                                                                                                                             |                                                                                                                           |
c.   Create and label a graph for your table.
d.   Interpret the points
$$(0, 0)$$
and
$$(1, r) $$
from the graph in context of the situation.


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