Let's consider another similar situation: we have two paints, yellow and blue. In order to get green color we have to mix blue and yellow paints at a special ratio. For example, 1 liter of yellow paint and 2 liters of blue paint give us necessary green paint (1:2 ratio). In other words, we can get green paint only if we follow strictly the ratio, otherwise resulted paint will contain more blue or more yellow. In our example, if we have 20 litters of yellow paint, we should get 40 litters of blue paint, not more or less. If we make 60 litters of green paint, we should take 20 liters of yellow and 40 litters of blue.

The same reasoning in the problem. We know all concentrations. Therefore, we have a special ratio of initial mixtures in order to get resulted mixture. knowing amount only one mixture is enough to find others using the ration.

By the way, this problem

7-t75289 uses the same idea. So, you can solve it very quickly.

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