Annulus Area

Weekly Problem 38 - 2011
Given three concentric circles, shade in the annulus formed by the smaller two. What percentage of the larger circle is now shaded?
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Problem



The three circles in the diagram have the same centre and have radii 3cm, 4cm and 5cm. What percentage of the larger circle is shaded?

Image
Annulus Area

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.