Corrine wrote temperatures in degrees Celsius and the equivalent temperatures in degrees Fahrenheit.Equivalent TemperaturesCelsius–1051020Fahrenheit14415068Which explains how Corrine could determine if the temperatures vary directly?

For two quantities to vary directly, their ratio must stay constant: Fahrenheit ÷ Celsius should be the same for every pair. Corrine can compare the equivalent temperatures as ratios; if those ratios are equal, the temperatures vary directly. A straight-line graph alone is not enough, because a direct variation must also pass through the origin.

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