The game of Scoring is very simple: the board is a strip of several squares (parameter Heap size), on which there are placed several chips (whose number is controlled by the parameter # Counters).
http://www.cut-the-knot.org/recurrence/Scoring.shtml
Select exactly one square in every row and in every column and check that the sum (or the product) of numbers in the selected squares does not depend on your selections.
http://www.cut-the-knot.org/Curriculum/Arithmetic/ArithmeticMagicMatrix.shtml
Let N be an integer. This is the lone number at the bottom of the applet below. It can be modified by clicking on it. Currently it is 4. For practical reasons, it can change between 3 and 6, inclusive.
http://www.cut-the-knot.org/Curriculum/Magic/Bachet.shtml
Take a wire stretched between two posts, and have a large number of birds land on it at random.
http://www.cut-the-knot.org/Curriculum/Probability/BirdsOnWire.shtml
In the applet, select box. One of the two balls it contains will pop up. After which you'll have to drag labels (they will appear at the right moment) into the empty label locations on the boxes.
http://www.cut-the-knot.org/SimpleGames/PickLabel.shtml
Compte de Buffon in the 18th century posed and solved the very first problem of geometric probability.
http://www.cut-the-knot.org/Curriculum/Probability/Buffon.shtml
Every 4th year is leap unless it's divisible by 100. This is only true with one additional caveat: among those divisible by 100, the ones that are divisible by 400 are still leap.
http://www.cut-the-knot.org/SimpleGames/Calendar.shtml
Children with bigger feet spell better. In areas of the South those counties with higher divorce rates generally have lower death rates.
http://www.cut-the-knot.org/do_you_know/misuse.shtml
In the applet below, lines may be dragged as a whole or with one of the two defining points. When a line is dragged or clicked upon one of its equations is displayed just beneath the graph.
http://www.cut-the-knot.org/Curriculum/Calculus/StraightLine.shtml
This is a two person game. You play against your computer. The board consists of a row of nine squares with a 4-letter word in each.
http://www.cut-the-knot.org/SimpleGames/SoupFish.shtml