Two concentric circles form a ring. The inner and outer circumferences of ring a

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Question
Two concentric circles form a ring. The inner and outer circumferences of ring are 5187 m and 3527 m respectively. Find the width of the ring.
Options
A. 4
B. 5
C. 6
D. 7

Correct Answer

4

Explanation

Let the inner and outer radii be r and R metres.

Then $2 ?R = \frac{352}{7} = > R = \frac{352}{7} * \frac{7}{22} * \frac{1}{2} = 8 m$

$2 ?R = \frac{528}{7} = > R = \frac{528}{7} * \frac{7}{22} * \frac{1}{2} = 12 m$

=> Width of the ring = (R - r) = (12 - 8) m = 4 m.

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Area problems

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1. A tank is 25 m long, 12 m wide and 6 m deep. The cost of plastering its walls and bottom at 75 paise per sq. m, is:
Options
A. rs.458
B. rs,558
C. rs.658
D. rs.758

6. If the radius of a circle is decreased by 50% , find the percentage decrease in its area.
Options
A. 75%
B. 65%
C. 35%
D. 25%

8. Find the perimeter of the rectangle or square with the given dimensions l = 5 feet, w = 2 feet?
Options
A. 11ft
B. 13ft
C. 14ft
D. 15ft

10. In a wheelchair slalom event, athletes weave around cones and race to the finish line. A diagram of the rectangular course is shown. Find the perimeter of the course
Options
A. 32
B. 42
C. 62
D. 92

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