The Total solution for NCERT class 6-12
Let the radius of a circle be r.Circumference of a circle = 2πrLet the radii of two circles are r1 andr2 whosevalues are 15 cm and 18 cm respectively.i.e., r1 = 15 cmand r2 = 18 cmNow, by given condition,Circumference of circle = Circumference of first circle + Circumference of secondcircle⇒ 2πr = 2π r1 + 2πr2 =⇒ r = r1 + r2⇒ r = 15 + 18∴ r = 33cmHence, required radius of a circle is 33 cm.