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Example

Solving a Two-Number Problem Using "Sum" and "More Than"

Apply the seven-step problem-solving strategy to a number problem involving two unknown numbers that are related by a "more than" phrase and whose sum is given.

Problem: One number is five more than another. The sum of the numbers is 2121. Find the numbers.

  1. Read the problem.
  2. Identify what to find: two numbers.
  3. Name the unknowns using a single variable. Let nn = the first number. Because one number is "five more than" the other, the second number is n+5n + 5.
  4. Translate into an equation: The sum of the two numbers is 2121, so:

n+(n+5)=21n + (n + 5) = 21

  1. Solve the equation. First, combine the like terms n+n=2nn + n = 2n:

2n+5=212n + 5 = 21

Subtract 55 from both sides:

2n=162n = 16

Divide both sides by 22:

n=8n = 8

Find the second number: n+5=8+5=13n + 5 = 8 + 5 = 13.

  1. Check: Is 1313 five more than 88? 8+5=138 + 5 = 13 \checkmark. Is their sum 2121? 8+13=218 + 13 = 21 \checkmark.
  2. Answer: The numbers are 88 and 1313.

This example illustrates a key technique for two-unknown number problems: express both quantities through a single variable using the stated relationship ("five more than" becomes n+5n + 5), then write an equation from the remaining fact (the sum). The resulting equation involves combining like terms before using inverse operations to isolate the variable.

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Updated 2026-04-21

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