Multiple choice

Assume a circle with diameter = 2r. If its radius is doubled, then find the new area and find the ratio of the areas of old circle to the new circle.

  1. 2 * pi * r * r ; 1/2

  2. 4 * pi * r * r ; 1/4

  3. pi * r * r ; 1/4

  4. (pi * r * r)/2 ; 1/2

  5. 2 * pi * r * r ; 1/4

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Diameter of old circle = 2 r Radius = r Area = pi * radius * radius Radius of new circle = 2 r Area of new circle = pi * 2 r * 2r                      => pi * 4 * radius * radius Ratio = area of old circle / area of new circle            => 1/4

Ans. 4 * pi * r * r ; 1/4