Data Sufficiency

A circle has the same area with a rectangle. What is the circumference of the circle?
1) The perimeter of the rectangle is 18
2) The area of the rectangle is 20

*An answer will be posted in 2 days.

We can modify the original condition and the question. The area of the circle and the area of the rectangle are same. Hence, since it is asking for the circumference of the circle, we only have to know the area of the circle (which is same as the area of the rectangle). So, the correct answer is B.

- Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Max@Math Revolution wrote:A circle has the same area with a rectangle. What is the circumference of the circle?
1) The perimeter of the rectangle is 18
2) The area of the rectangle is 20

*An answer will be posted in 2 days.

(1) Not sufficient - the area of the rectangle can vary depending on the lengths of the sides. Since there is no fixed area, there is no way to use the information to determine the area of the circle.

(2) Sufficient - the circle must have an area of 20. From this, one could determine the radius. And then use the calculated radius to determine the circumference of the circle.

Answer is B.[/spoiler]