Question

Jackie earned a total of $9 by selling 3 cups of lemonade. How many cups of lemonade does Jackie need to sell in all to earn $18? Assume the relationship is directly proportional

Answer 1

6 cups

Explanation:

When two things are directly proportional (e.g. y and x), we can model the relationship with the direct variation equation, which is

y = kx, where

• k is the constant of proportionality

Step 1: To find k, we can allow y to represent Jackie's total revenue from selling lemonade ($9) and x to represent the quantity of cups of lemonade sold ($3):

9 = 3k

k = 3

Step 2: Now that we've found the constant of proportionality, we can plug in 18 for y and 3 for k, allowing us to solve for x:

18 = 3x

6 = x

Thus, in order for Jackie to earn $18, she must sell 6 cups in all.