Count the sides

Choose only from triangles and squares. How many of each shape do you need to make these?

a. Two shapes with a total of 8 sides.

b. Three shapes with a total of 10 sides.

c. Four shapes with a total of 12 sides.

d. Five shapes with a total of 17 sides.

e. Six shapes with a total of 22 sides.

Age 13-15

Six coins

Six coins are arranged with their centres in a circle so that each touches the two adjacent ones.

What is the radius of the circle that will just enclose the six coins?

Brainteaser solutions from page 30

Count the sidesa 2 squares b 1 square and 2 triangles c 4 triangles d 2 squares and 3 triangles e 4 squares and 2 triangles Six coins If the coin has a radius c, then the circle has a radius 3c.