Using the proportionality concept, it is found that the value of y is 20 when x = 15.
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The variables x and y are directly proportional, which means that:
[tex]y = cx[/tex]
In which c is the constant of proportionality.
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y=4 when x=3
We use this to find the constant, thus:
[tex]y = cx[/tex]
[tex]3c = 4[/tex]
[tex]c = \frac{4}{3}[/tex]
Thus:
[tex]y = \frac{4x}{3}[/tex]
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When x = 15.
[tex]y = \frac{4 \times 15}{3} = 4 \times 5 = 20[/tex]
The value of y is 20 when x = 15.
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