Using cross products, we'd ask ourselves if four times five equaled three times seven. Since it does not, we can assert that the two fractions are NOT proportional. You can reduce each fraction. Sometimes one of the parts of the proportion is missing. So to look at a more concrete example, we see that we can set the cross-products equal, then solve the resulting equation.
Proportions are often helpful when solving word problems.
If you hear two comparisons of like quantities within a word problem, try setting up a proportion. So 10 cups of flour would be needed to bake 5 loaves of bread. Take me to some more Fast Facts. On Line Home Page.