Proportion Calculator

A proportion states that two ratios are equal, and this solves one when any single term is missing. Leave the unknown blank and it returns that term, the completed proportion, the value both ratios share and the cross products that prove it. A second action takes four known terms and says whether they are in proportion and how far out they are if they are not, while a third handles inverse proportion, where the product rather than the ratio stays fixed. That last case is the one people get wrong: four workers taking six days means three workers take eight days, not four and a half.