Selina Concise Class 8 Math Chapter 20 Area of a Trapezium and a Polygon Exercise 20D Solution

(1) Find the radius and area of a circle, whose circumfarence is:

(i) 132 cm

(ii) 22 m

(2) Find the radius and circumference of a circle whose area is:

(ii) 154 cm square

(ii) 6.16 m square

(3) The circumfarence of a circular table is 88 m. Find its area.

(4) The area of a circle is 1386 square centimeter, find its circumfarence.

(5) Find the area of a flat circular ring formed by two concentric circles (circles with same centre) whose radii are 9 cm and 5 cm.

(6) Find the area of the shaded portion in each of the following diagrams:

Solution:

(7) The radii of the inner and outer circumfarences of a circular-running track are 63 m and 70 m respectively. Find:

(i) the area of the track

(ii) the difference between the lengthsof the two circumfarences of the track

(8) A circular field of radius 105 m has a circular path a uniform width of 5 m along and inside its boundary. Find the area of the path.

Solution:

(9) There is a path of uniform width 7 m round and outside a circular garden of diameter 210 m. Find the area of the path.

(10) A wire, when bent in the form of a square, encloses an area of 484 cm square. Find:

(i) one side of the square

(ii) length of the wire

(iii) the largest area encloses, if the same wire is bent to form a circle.

(11) A wire, when bent in the form of a square, encloses an area of 196 cm square. If the same wire is bent to forn a circle, find the area of the circle.

Solution:

(12) The radius of a circular wheel is 42 cm. Find the distance travelled by it in:

(i) 1 revolution

(ii) 50 revolutions

(iii) 200 revolutions

(13) The diameter of the wheel of a car is 0.70 m. Find the distance covered by it in 500 revolutions.

If the wheel ts 5 minutes to make 500 revolutions, find its speed in:

(i) m/s

(ii) km/hr

(14) A bicycle wheel, diameter 56 cm, is making 45 revolutions in every 10 seconds. Calculate the speed, in kilometre per hour. of the bicycle.

Solution:

(15) A roller has a diameter of 1.4 m. Find :

(i) its circumfarence

(ii) the number of revolutions it makes while travelling 61.6 m.

(16) Find the are of the circle, length of whose circumfarence is equal to the sum of the lengths of the circumfarences of circles with radii 15 cm and 13 cm.

(17) A piece wire of length 108 cm is bent to form a semicircular arc bounded by its diameter. Find its radius and encloses area.

Solution: 

(18) In the following figure, a rectangle ABCD encloses three circles. If BC = 14 cm, find the area of the shaded portion. (Take π = 3 1/7)

Solution:


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