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SAI International School


                                                 Sub – Mathematics

                                                      Class - IV


                                                 Topic – Geometry

        Sub-topic 7 : - Relation between radius and diameter


             Introduction – If you keep two radii in a straight line, a diameter is formed. So, diameter is
               twice of its radius. The radius is half of its diameter.

















               Radii = OA, OB
               Diameter = AB (OA + OB)
             To find out radius, when diameter is given.

                         Radius =




               Example 1: find the radius of the circle, if diameter is 16 cm.

               Solution: radius =       = 8 cm.

               Example 2: find the radius of the circle, if the diameter is 20 m.

               Solution:  radius =       = 10 cm.

             To find out diameter, when radius is given.

                     Diameter = 2 x Radius



                Example 1 : find the diameter of the circle, if the radius is 12 cm.
               Solution : diameter = 2 x radius = 2 x 12 cm = 24 cm
               Example 2 : find the diameter of the circle, if the radius is 6 m.
               Solution : diameter = 2 x radius = 2 x 6 m = 12 m
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