Example

Solving a Punch Mixture Problem by Graphing

Apply the seven-step problem-solving strategy to solve a real-world mixture problem by graphing a system of linear equations.

Problem: Sondra is making 10 quarts of punch from fruit juice and club soda. The number of quarts of fruit juice is 4 times the number of quarts of club soda. How many quarts of fruit juice and how many quarts of club soda does Sondra need?

  1. Read the problem.
  2. Identify what to find: the number of quarts of fruit juice and the number of quarts of club soda.
  3. Name the unknowns: Let ff represent the number of quarts of fruit juice. Let cc represent the number of quarts of club soda.
  4. Translate into a system of equations.
    • The total amount of punch is 10 quarts: f+c=10f + c = 10.
    • The fruit juice is 4 times the club soda: f=4cf = 4c.
    • The system is: {f+c=10f=4c\left\{\begin{array}{l} f + c = 10 f = 4c \end{array}\right.
  5. Solve by graphing both equations on the same coordinate system. Plotting with cc on the horizontal axis and ff on the vertical axis:
    • The line f=4cf = 4c has a slope of 4 and a y-intercept of (0, 0).
    • The line f+c=10f + c = 10 can be rewritten as f=c+10f = -c + 10, with a slope of -1 and a y-intercept of (0, 10).
    • The two lines intersect at the point (2, 8), which corresponds to c=2c = 2 and f=8f = 8.
  6. Check: Is 8 quarts of fruit juice 4 times 2 quarts of club soda? 4×2=84 \times 2 = 8, which is correct. Do 8 quarts of fruit juice plus 2 quarts of club soda equal 10 quarts of punch? 8+2=108 + 2 = 10, which is also correct.
  7. Answer: Sondra needs 8 quarts of fruit juice and 2 quarts of club soda.

This example demonstrates how a mixture scenario naturally produces two equations—one from a total-quantity constraint and one from a multiplicative relationship—that form a system solved by graphing.

Image 0

0

1

Updated 2026-06-26

Tags

OpenStax

Elementary Algebra @ OpenStax

Ch.5 Systems of Linear Equations - Elementary Algebra @ OpenStax

Algebra

Math

Prealgebra

Related
Learn After