Estimation Game
A Java game that pits you against the clock in a game of estimating. Estimation is something people get into a pickle about so a quick burst of this as a warm up in an IT room might get students more ready to make quick guesses. The Java game sometimes gives problems like 567 + 2, but most of the time, they are three full digits in the 100s.
What I like about the game is the combination of working against the clock and being as accurate as possible Рthe points depend on both. This feature of the game play may lead to reflection on the best calculation strategy for a given purpose Рe.g. in a meeting, it might be important simply to know if the total cost of some project is £1000 or £2000, but later, precise costs will have to be recorded.