Speakout Advanced p 21. Brain Teasers. Extra Listening.

How to get correct advice when you can only ask one question from either a liar or a truthteller (when you don't know who is what).

The Kahn Academy has now posted on YouTube over 800 videos (find a complete list here) that will teach students the ins-and-outs of algebra, geometry, trigonometry, calculus, statistics, finance, physics, economics and more.