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The bull's eye of a target is a circle 20 cm
in diameter. It is surrounded by four rings each 15 cm wide. Find the area of each ring.
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The rings so formed are called Annulus.
The method to calculate the area of each annulus would be as follows:-
The first cirle after the bull's eye has a radius of 17.5 cm.
The bull's eye has a radius of 10 cm.
Hence, the area of the first ring would be
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If two concentric circles have radii r[sub]1[/sub] and r[sub]2[/sub] (r[sub]1[/sub] < r[sub]2[/sub]), the area of the ring in between (called an annulus) is π(r[sub]2[/sub][sup]2[/sup]−r[sub]1[/sub][sup]2[/sup]).
And ganesh, the 17.5 is wrong it should be 12.5.
Last edited by JaneFairfax (2007-03-11 05:44:37)
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Think harder! the solution will be obvious when you draw the graph
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how do you do that
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Incidentally, you can also work out the area of an annulus by finding the length of the red line shown below, then finding the area of a circle with that length as the diameter.
Of course, finding that length in the first place is quite tricky, so that method might not be too useful.
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