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?
This is part of our collection of Short Problems.
You may also be interested in our longer problems on Perimeter, Area and Volume: Age 14-16.
We have put together a selection of these short problems as printable worksheets:
Printable worksheets: Age 14-16 ⭐ Printable worksheet: Age 14-16 ⭐⭐ Printable worksheet: Age 14-16 ⭐⭐⭐ Printable worksheet solutions
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?
Can you work out the fraction of the larger square that is covered by the shaded area?
Boris' bicycle has a smaller back wheel than front wheel. Can you work out how many revolutions the front wheel made if the back wheel did 120,000?
Weekly Problem 9 - 2016
The diagram to the right shows a logo made from semi-circular arcs. What fraction of the logo is shaded?
The circle of radius 4cm is divided into four congruent parts by arcs of radius 2cm as shown. What is the length of the perimeter of one of the parts, in cm?
At the corner of the cube circular arcs are drawn and the area enclosed shaded. What fraction of the surface area of the cube is shaded? Try working out the answer without recourse to pencil and paper.
Imagine cutting out a circle which is just contained inside a semicircle. What fraction of the semi-circle will remain?
Rotating a pencil twice about two different points gives surprising results...
Of these five figures, which shaded area is the greatest? The large circle in each figure has the same radius.
A square is divided into four rectangles and a square. Can you work out the ratio of the side lengths of the rectangles?
Weekly Problem 11 - 2007
A circle of radius 1 rolls without slipping round the inside of a square of side length 4. Find an expression for the number of revolutions the circle makes.
Tom and Jerry start with identical sheets of paper. Each one cuts his sheet in a different way. Can you find the perimeter of the original sheet?
Three circles have been drawn at the vertices of this triangle. What is the area of the inner shaded area?
Weekly Problem 30 - 2011
Three touching circles have an interesting area between them...
The diagram shows a shaded shape bounded by circular arcs. What is the difference in area betweeen this and the equilateral triangle shown?
The diagram shows four equal discs and a square. What is the perimeter of the figure?
Weekly Problem 26 - 2015
What are the volume and surface area of this 'Cubo Vazado' or 'Emptied Cube'?
The diagram shows 8 circles surrounding a region. What is the perimeter of the shaded region?
Weekly Problem 34 - 2015
Four tiles are given. For which of them can three be placed together to form an equilateral triangle?
Can you find the shortest distance between the semicircles given the area between them?
What is the ratio of the areas of the squares in the diagram?
A solid metal cone is melted down and turned into spheres. How many spheres can be made?
When the roll of toilet paper is half as wide, what percentage of the paper is left?
Two similar cylinders are formed from a block of metal. What is the volume of the smaller cylinder?
Draw two circles, each of radius 1 unit, so that each circle goes through the centre of the other one. What is the area of the overlap?
Weekly Problem 5 - 2006
How many times does the inside disc have to roll around the inside of the ring to return to its initial position?
Weekly Problem 13 - 2006
If three runners run at the same constant speed around the race tracks, in which order do they finish?
Weekly Problem 52 - 2014
Four arcs are drawn in a circle to create a shaded area. What fraction of the area of the circle is shaded?
Weekly Problem 15 - 2015
In the diagram, two lines have been drawn in a square. What is the ratio of the areas marked?
Weekly Problem 51 - 2015
Charlie is making clown hats from a piece of cardboard. What is the maximum number he can make?
Two vases are cylindrical in shape. Can you work out the original depth of the water in the larger vase?
Cutting a rectangle from a corner to a point on the opposite side splits its area in the ratio 1:2. What is the ratio of a:b?