Videos Cliff Johnson - 15 Oct 2015 Videos to watch Averages: Introduction to averages and algebra problems involving averages. Multiple rates word problem: Sometimes you'll need to solve for multiple parts of the equation before getting at the answer. Here we solve for average speed, but first we have to determine total distance and total time. Logic challenge You have a balance scale and 9 coins, all exactly the same weight except one is slightly lighter. How can you determine which of the coins is lighter in only 2 weighings? Math challenge Is 1001 prime? What about 10001? And 10101? Just for fun