Problem 12 · 2019 Math Kangaroo
Medium
Algebra & Patterns
sum-constraintcasework
All dogs are equally heavy. The two balance scales are shown in the picture. How much could one dog weigh?
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Answer: E — 11 kg
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Hint 1 of 2
On the first scale the 12 kg side goes down, so one dog is lighter than 12 kg.
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Hint 2 of 2
On the second scale the two-dog side goes down, so two dogs together are heavier than 20 kg.
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Approach: use which side of each scale tips down
- The first scale tips toward the 12 kg weight, so one dog must weigh a little less than 12 kg.
- The second scale tips toward the two dogs, so the two dogs together weigh more than 20 kg, which means one dog weighs more than 10 kg.
- The only whole number of kilograms that is more than 10 but less than 12 is 11 kg (E).
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