What I Have Learned
Equal ratios form a proportion. A proportion is an equality
between two ratios. The inner term (2nd and 3rd) are called means while
the outer terms (1st and 4th) are called extremes.
In a proportion, the product of the means equals to the product
of the extremes.
We can use cross product to determine whether two ratios form a
proportion and to find the missing term in a proportion.
A proportion is said to be direct if as one term increases, the
other term also increases in the same rate or as one term decreases, the
other term also decreases at the same rate.​