Problem 5 · 2015 Math Kangaroo
Easy
Algebra & Patterns
substitution
The two shapes below each stand for a number. The red triangle plus 4 equals 7, and the blue square plus the red triangle equals 9. Which number is hidden behind the square?
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Answer: E — 6
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Hint 1 of 2
The first picture-sum tells you the triangle's number all by itself.
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Hint 2 of 2
Once you know the triangle, use the second picture-sum to find the square.
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Approach: find the triangle first, then use it to find the square
- Triangle and 4 make 7, so the triangle must be 3 (because 3 + 4 = 7).
- The square and the triangle make 9, so the square and 3 make 9.
- The number that goes with 3 to make 9 is 6 (since 6 + 3 = 9).
- The hidden number is 6.
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