Example

Example: Solving a Stamp Mixture Problem with 49-Cent and 20-Cent Stamps

Apply the seven-step problem-solving strategy and the total-value model to a stamp mixture problem to find the numbers of two different stamps when their total cost is known.

Problem: Kailee paid $14.74 for stamps. The number of 49-cent stamps was four less than three times the number of 20-cent stamps. How many 49-cent stamps and how many 20-cent stamps did Kailee buy?

  1. Read the problem and identify the types involved: 49-cent stamps (worth $0.49 each) and 20-cent stamps (worth $0.20 each). The total value is $14.74.
  2. Identify what to find: the number of 49-cent stamps and the number of 20-cent stamps.
  3. Name the unknowns using a single variable. Let xx = the number of 20-cent stamps. The phrase "four less than three times" translates to 3x43x - 4. Therefore, the number of 49-cent stamps is 3x43x - 4.
  4. Translate into an equation: 0.49(3x4)+0.20x=14.740.49(3x - 4) + 0.20x = 14.74
  5. Solve the equation:
  • Distribute 0.490.49: 1.47x1.96+0.20x=14.741.47x - 1.96 + 0.20x = 14.74
  • Combine like terms: 1.67x1.96=14.741.67x - 1.96 = 14.74
  • Add 1.961.96 to both sides: 1.67x=16.701.67x = 16.70
  • Divide both sides by 1.671.67: x=10x = 10

Find the number of 49-cent stamps: 3(10)4=304=263(10) - 4 = 30 - 4 = 26. 6. Check: Does 10(0.20)+26(0.49)=14.7410(0.20) + 26(0.49) = 14.74? 2.00+12.74=14.742.00 + 12.74 = 14.74 14.74=14.7414.74 = 14.74 \checkmark 7. Answer: Kailee bought 1010 20-cent stamps and 2626 49-cent stamps.

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Updated 2026-04-22

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