Question:The circumference of a circle is 88 m. Find its area. 

`2 πR = 88 => 2 xx 22/7 xx R = 88`

`:. R = (88 xx 7/44) = 14 m.`

:. Area` = π R^2 = (22/7 xx 14 xx 14) m^2`

           `= 616 m^2`

Question:The area of a circle is 154 `cm^2`. Find its circumference. 

`π R^2 = 154 => 22/7 xx R^2`

`= 154 or R^2 = (154 xx 7/22)`

`= 7^2`

So, R = 7 cm.

:. Circumference` = 2 πR = (2 xx 22/7 xx 7) cm`

           `= 44 cm.`

Question:Two concentric circles form a ring. The inner and outer circumference of the ring are` 50 2/7` m and ` 75 3/7` m respectively. Find the width of the ring. 

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

Then, `2 π r = 352/7 => r = (352/7 xx 7/44)` 

   `= 8 m`

`2 πR = 528/7 => R`

`= (528/7 xx 7/44)`

`= 12 m`

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

Question:The inner circumference of a circular race track, 14 m wide, is 440 m. Find the radius of the outer circle. 

Let inner radius be r metres.

Then,` 2πr = 440 => r = (440 xx 7/44) = 70 m.`

:. Radius of outer circle` = (70 + 14) m`

                   `= 84 m`

Question:The diameter of the driving wheel of a bus is 140 cm. How many revolutions per minute must the wheel make in order to keep a speed of 66 kmph ? 

Distance to be covered in 1 min.

`= (66 xx 1000/60) m`

`= 1100 m.`

Circumference of the wheel 

`= (2 xx 22/7 xx 0.70) m`

`= 4.4`

:. Number of revolutions per min

`= (1100/4.4)`

`= 250`