Based on the TV show Countdown this is a nice mental arithmetic game that develops quick mental calculation skills. The rules are simple. You can use each of the numbers at the top of the page only once but can use any operation you know (multiply, divide, add, subtract, square, square root etc.) as many times as you want.
There are two target numbers set for the players to reach, one easy and one hard. The hyperlink at the bottom of the page is to link to a piece of suitably long music. I found the actual Countdown music by searching the Internet.