Mathematical Skills: Ability to add, subtract, multiply and divide in all units of measure, using whole numbers, common fractions, and decimals, Ability compute rate, ratio, and percent and to draw and interpret graphs. The Yukon-Kuskokwim Health Corporation is a Tribal health care organization, serving nearly 30,000 people living across rural, southwest Alaska in villages with populations from about 10 to more than 1,000.