SOLUTION: Three stones are weighed on a scale, two at a time. The scale shows weights of 49 kg, 63 kg, and 80 kg. How much does the heaviest stone weigh? (A) 30 kg (B) 36 kg (C) 40 kg (D)

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Question 206854: Three stones are weighed on a scale, two at a time. The scale shows weights of 49 kg, 63 kg, and 80 kg. How much does the heaviest stone weigh?
(A) 30 kg (B) 36 kg (C) 40 kg (D) 47 kg (E) Not enough
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Answer by Alan3354(69443) About Me  (Show Source):
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Three stones are weighed on a scale, two at a time. The scale shows weights of 49 kg, 63 kg, and 80 kg. How much does the heaviest stone weigh?
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a+b = 49
a+c = 63
b+c = 80
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a = 49-b Sub into eqn 2
49-b+c = 63
-b+c = 14
b+c = 80 eqn 3
----- Add
2c = 94
c = 47 kg
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b = 33 kg
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a = 16 kg