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 Amsco Integrated Algebra I: Direct Variation
This is a free lesson from our course in Amsco's Integrated Algebra
This lesson explains direct variation. A direct variation is a relationship between two variables such that their ratio is always constant. In every direct variation, we say that one variable varies directly as the other, or that one variable is directly proportional to the other. The constant ratio is called a constant of variation. The formula normally used for direct variation is y = kx, where k is the constant of variation. This equation can be read: ‘y varies directly as x’. If you are to solve for k, divide both sides of the equation by x. It works out to k = (y/x). Note that here y is numerator and x is denominator. (More text below video...)
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(Continued from above) For example: Given: the weekly salary Emily earns (P), varies directly as the number of hours, h, which she works. If you are required to express this relationship, follow the steps given below: As above, the formula for direct variation is y = kx, where k is the constant of variation.
Since P varies directly as h in the question, let y = P and x = h in equation y = kx i.e. replace y with P and x with h, leaving k as it is. Now write the relation between P and h as a formula P = kh.
You get the final answer- P = kh
Take a look at the video above for detailed explanations of Ratios.

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