Try to beat the time!
You've got 10 seconds to start. Answer questions to get more time, and don't let the clock run out.
Test it yourself over here at http://www.mental-math-trainer.com
https://news.ycombinator.com/item?id=8664180
http://www.learn-swiss-german.ch/ http://www.schweizerdeutsch-lernen.ch/ http://www.michael-jakob.com/