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Grade 8 puzzle 11: Counting the complement

A free grade 8 math puzzle that teaches Counting the complement. Try it first — the hint and the full solution open when you are ready.

Problem 11 · Counting the complement · 3 points

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A chameleon’s scarf has three patches numbered 1, 2, and 3. Each patch can be gold, teal, pink, or purple; how many different scarves have at least one gold patch?

Illustration for problem 11
  1. 36
  2. 64
  3. 48
  4. 37
  5. 27
Show a hint
  • Count all possible scarves first.
  • Subtract those with no gold patches.
Show the answer and solution

Answer: D — 37

Each of the three patches has 4 choices, giving 4 × 4 × 4 = 64 scarves. With no gold, each patch has 3 choices, giving 3 × 3 × 3 = 27 scarves. So the answer is 64 − 27 = 37. The tempting answer 48 comes from choosing which patch is gold and then coloring the other two, but it counts scarves with multiple gold patches more than once.

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