Two circles have a radius difference of 7 cm and an area difference of 1078 sq cm. What is the radius of the smaller circle_________?
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Answer: B. 21cm
Explanation
The difference in area is pi times R squared minus r squared, which factorises to pi times the sum and the difference of the radii. With the difference at 7 and the area difference at 1078, the sum of the radii is 1078 divided by 22, or 49. Solving 49 and 7 together gives the larger radius as 28 and the smaller as 21 centimetres.
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- Mathematics
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- Mathematics
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- Difficulty
- medium
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