document.write( "Question 238034: The radius of a circle whose circumference is equal to the sum of the circumferences of the two circles of diameters 36cm and 20 cm is
\n" ); document.write( "(A) 56 cm (B) 42 cm (C) 28 cm (D) 16 cm
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Algebra.Com's Answer #174936 by anantha(86)\"\" \"About 
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sol:
\n" ); document.write( "in this problem 3 circles are given
\n" ); document.write( "let the radius of the 1 st circle be r
\n" ); document.write( "circumference of 1st circle=2*pi*r
\n" ); document.write( "and diameter of the 2nd circle=36cm
\n" ); document.write( "circumference of 2nd circle=pi*diameter of 2nd circle=pi*36=36pi
\n" ); document.write( "diameter of the 3rd circle=20cm
\n" ); document.write( "circumference of the 3rd circle=pi*20=20pi
\n" ); document.write( "according to the problem
\n" ); document.write( "circumference of 1st circle=circumference of 2nd circle +circumference of 3rd circle
\n" ); document.write( "2*pi*r=36pi+20pi
\n" ); document.write( "2*pi*r=56pi
\n" ); document.write( "dividing both sides by pi
\n" ); document.write( "2*pi*r/pi=56pi/pi
\n" ); document.write( "2r=56
\n" ); document.write( "dividing both sides by 2
\n" ); document.write( "2r/2=56/2
\n" ); document.write( "r=28cm\r
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