The document discusses ratios and proportions. It provides examples of expressing ratios using words, colons, and fractions. It explains using cross products to determine if two ratios are proportional. The example problem asks how many unregistered extraterrestrials there are given that the ratio of unregistered to registered is 7:5 and there are 2,280 registered extraterrestrials. Using this ratio and cross products, the number of unregistered extraterrestrials is calculated to be 3,192.