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Define A and B:
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Let A be the volume of the liquid in container A at first.
Let B be the volume of the liquid in container B at first.
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Construct equation :
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2 containers have the same liquid.
⇒ A = B
120 ml is then poured from A to B. Container B now contains 4 times as much liquid as A.
⇒ 4(A - 120) = (B + 120)
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Solve A and B :
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A = B ------- (1)
4(A - 120) = (B + 120) ----- (2)
Sub (1) into (2) :
4(B - 120) = (B + 120)
4B - 480 = B + 120
3B = 480 + 120
3B = 600
B = 200
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Find A and B :
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B = 200 ml
A = B = 200 ml
Container A at the end = 200 - 120 = 80ml
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Answer: Container A has 80m left.
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