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The ratio of copper and zinc in an alloy is 9:7. If the weight of zinc in the alloy is 9.8 kg, find the weight of copper in the alloy in kg.

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Hint: In this question, we use the concept of ratio and proportion. Let the weight of copper in terms of variable then use the weight of zinc in the alloy.

Complete step-by-step answer:

Given, weight of zinc in the alloy =9.8kg
We know the ratio of copper and zinc in an alloy is 9:7
Let the weight of copper in an alloy =9x
Let the weight of zinc in an alloy =7x
Now, we also know the actual weight of zinc in the alloy so put the weight of zinc equal to 7x.
$
   \Rightarrow 7x = 9.8 \\
   \Rightarrow x = \dfrac{{9.8}}{7} \\
   \Rightarrow x = 1.4kg \\
 $
To find the weight of copper in an alloy then use the value of x=1.4 kg
Weight of copper in an alloy =9x
$
   \Rightarrow 9 \times 1.4 \\
   \Rightarrow 12.6 kg \\
$
So, the weight of copper in the alloy is 12.6 kg.

Note: Whenever we face such types of problems we use some important points. First we assume the weight of components (copper and zinc) of an alloy with the help of ratio given in the question then put the assumed weight of zinc equal to actual weight of zinc given in the question. So, we will get the required answer.