Find the the area of a circular ring Whose outer diameter is 10 cm and inner diameter is 6 diameter?
- 4pi cm^2
- 16pi cm^2
- 64pi cm^2
Explanation
The ring area is the outer circle area minus the inner. With outer radius 5 and inner radius 3, this is pi(5^2 - 3^2) = pi(25 - 9) = 16pi cm^2. Subtracting diameters or radii before squaring would give the wrong result.
tini1992 asking:
How come? A get 64 out from R^2-r^2
Community Comments (2)
D
dimky Posts: 514 27.11.2016 / 19:33
Hi.
Area of a ring is pi * (R^2 - r^2)
Area in this question is = pi * (25 - 9) = pi * 16 cm^2
Area of a ring is pi * (R^2 - r^2)
Area in this question is = pi * (25 - 9) = pi * 16 cm^2
Z
zoom77 Posts: 6 19.04.2017 / 16:18
thats right; the area of a circular ring is calculated by the formula pi*(R^2-r^2)
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