Question

Given the proportion 45: 75 :: 75: 125, what is the mean proportion?

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Answer 1

$45:75::75:125$ can be written as $\frac{45}{75}$ =$\frac{75}{125}$
The four parts of the proportion are separated into two groups, the means and the extremes, based on their arrangement in the proportion. Reading from left-to-right and top-to-bottom, the means are the second and third numbers. Therefore, the mean proportion is $75$.