What was required for me to do a Mastery Challenge

This specific mastery challenge required for me to know how to solve certain equations. For example, if 5 things make up 2% of an entire group of things, how many things are neccesary to make 100% of the group? To solve this type of problem, divide the number of things you have by the percentage to get how many things are in 1%. Then, multiply the quotient by 100 to get 100% of the answer. Another thing I need to know was how to solve proportion word problems. For example, if 90 cartridges are needed for three paintgun pistols, how many cartridges are needed for 10 pistols? I can figure out which is the correct equation by looking at the problem in an equation in my mind. If 90 cartridges fill three pistols, then 30 cartridges can fill one pistol. Multiply 30 cartridges by 10 pistols to get the answer.