You can move the 4 pieces of the jigsaw and fit them into both
outlines. Explain what has happened to the missing one unit of
How far have these students walked by the time the teacher's car
reaches them after their bus broke down?
Experiment with the interactivity of "rolling" regular polygons, and explore how the different positions of the red dot affects the distance it travels at each stage.
Sheila Luk (Year 10, The Mount School, York) saw right through
this 'deception' and gave an excellent explanation of the
The cheat is that although each triangle has a side of length 1
cm, the side at right angles to it is of length 10/
11 cm. The diagonal of the rectangle does not go through
the corners of the squares if it's drawn on squared paper.
The new rectangle, shown dotted, is not 11 by 10, but 10
10/ 11 by 10 and the difference in area is
exactly 10/ 11 square cm, the area of the two
triangles which were removed.
10 10/ 11 x 10 = 109 1/
11= 110 - 10/ 11