Algebra 1
Unit 5
Direct Variation and Application Practice
Name __________________________________________
Is each equation a direct variation? If it is, find the constant of variation.
For the data in each table, tell whether y varies directly with x. If it does, write an equation for the direct variation.
1. The amount of simple interest earned in a savings account varies directly with the amount of money in the savings
account. You have $1000 in your savings account and earn $50 in simple interest.
a) Define the variables
b) Write a direct variation equation
c) How much interest would you earn if you had $1500 in a savings account?
2. Charles’s Law states that at constant pressure, the volume of a fixed amount of gas varies directly with its
temperature measured in degrees Kelvin. A gas has a volume of 250 mL at 300° K.
a) Define the variables
b) Write a direct variation equation
c) What is the volume if the temperature increases to 420° K?
Application Problems:
1. Verizon charges $199 for the new iPhone. They then charge $40 per month for a data plan.
Write an equation that gives the total cost paid as a function of the number of months you will have the phone.
a) Define the variables:
b) Write the equation:
c) Find the total cost of having an iPhone for 8 months.
d) If a customer’s combined bill was $439, how many months did they have the phone for?
e) Graph the equation.
2. Anna buys $70 worth of flour and sugar for her bakery. A bag of flour costs $5, and a bag of sugar costs $7.
Write an equation in standard form to find how many bags of each item you must buy to spend $70.
a) Define the variables:
b) Write the equation:
c) Find the amount of flour bought if 5 bags of sugar were bought. (continued on next page)
d) Find the x-intercept and y-intercept to help you graph the equation.
3. Amy works at Starbucks and makes $50 each day. She also makes an additional $2 for every gift card she sells.
Write an equation that gives the total money made each day as a function of the number of gift cards sold.
a) Define the variables:
b) Write the equation:
c) Find the total amount Amy will make if she sells 5 gift cards.
d) If Amy made $72 yesterday, how many gift cards did Amy sell?
e) Graph the equation.
4. The French club wants to raise $150.00 to attend a special program at the Museum. The club decides to sell beignets
before school. Plain beignets will sell for $1.25, powered sugar beignets will sell for $1.75 each.
Write an equation in standard form to find how many beignets of each type you must sell to spend $150.
a) Define the variables:
b) Write the equation:
c) Find the number of plain beignets need to be sold if 5 powered sugar beignets were sold.
d) Find the x-intercept and y-intercept to help you graph the equation.
5.