Problem 9 · 2017 Math Kangaroo
Medium
Arithmetic & Operations
work-backward
Every box shows the result of the addition of the numbers on the very left and on the very top (for example: 6 + 2 = 8). Which number is written behind the question mark?
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Answer: E — 15
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Hint 1 of 2
Every box is its left number added to its top number; find a box where you already know both to fill in a missing edge number.
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Hint 2 of 2
The box showing 10 sits under the top number 2, so its left number must make 10.
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Approach: use a known box to find the missing left number, then add
- Each box is the number at the left of its row plus the number at the top of its column.
- The box showing 10 is under the top number 2, so its left number is 8 (because 8 + 2 = 10).
- The question-mark box is in that same row, under the top number 7.
- So it is 8 + 7 = 15.
Mark:
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