These two types of problems always involve two letters (usually x and y) and usually start the same way: if the problem has the words "varies directly" in it (or says two things are "proportional"), you just write down "y=kx" and start plug-and-chugging. If the problem says "varies inversely" (or variables are "inversely proportional"), you write down y=k/x and start plug-and-chugging. Sound too easy? What can I say: the same four steps will get you through every one of these things.
One Step Unit Conversion Problems
This video demonstrates a ton of basic unit conversion problems -- kilograms to grams, meters to millimeters, years to days -- as well as some funky word problems. What all these problems have in common is that only one conversion factor is needed to get the answer.
Simplifying Roots & Radicals
This video starts things off on the right foot with square roots, demonstrating the easiest and hardest-to-mess-up method for simplifying radicals, which is where we try and get the smallest number under the root as possible.
Areas of Triangles Inside Circles (SAT)
Oh man, if you plan on taking the SAT ever, this is definitely a video you're going to want to watch. Sure, it will help you in geometry class too, especially when you're looking at those crazy circle diagram problems. Circles and triangles: so different, yet they seem to always show up in the same problems.
Difficult Circular Region Area Problems (SAT)
Circles with other circles inside of them, "shaded regions", circles inscribed in squares, triangles inscribed in circles... If you're only going to watch one video about circle areas, this is the one becuase these problems are the type you'll see on standardized tests like the SAT.
Triangle Side Length Questions (SAT)
This is a type of problem that I didn't know what to call or where to put, yet it shows up in every geometry book and (most importantly) standardized tests. It's the problem type where they give you three numbers -- say 3,4,9 -- and ask you if those could be the sides of a triangle. Not sure why those particular three numbers don't work?
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)