An ant is moving around a few food pieces of different shapes scattered on the floor. For which food-piece would the ant have to take a longer round? Remember, circumference of a circle can be obtained by using the expression where r is the radius of the circle.
(a) Diameter = 2.8 cm Radius = Perimeter of a circle = ∴ Perimeter of the figure = + Diameter = = = 4.4 cm + 2.8 cm = 7.2 cm Note: In this figure, the diameter is also a part of the figure. (b) Perimeter of the semi-circular part =
= 4.4 cm Perimeter of ther remaining part = 1.5 cm + 2.8 cm + 1.5 cm = 5.8 cm ∴ Perimeter of the figure = 4.4 cm + 5.8 cm = 10.2 cm (c) Perimeter of the semi-circular part = ∴ Perimeter of the figure = 4.4 cm + 2 cm + 2 cm = 8.4 cm Since, 7.2 cm < 8.4 cm < 10.2 cm ∴ Perimeter of figure 'b' has the longest round. Note: In figures, 'b' and 'c', the diameters are not part of the figures.