A circle's radius is doubled. By what factor does its area change?
Answer and explanation
Correct answer: A. It is multiplied by 4
- Step 1: Area = pi x r^2. Step 2. (2r)^2 = 4r^2, so the area is 4 times larger. Answer: multiplied by 4. Why not the others: Area scales with the square of the radius, not linearly.
Practise more Geometry, Functions and Probability.
Free questions with an explanation for every one, and full timed ENEM Brazil mock tests.
More Geometry, Functions and Probability questions
- A wall 12 m long and 5 m high is painted with a paint that covers 6 square metres per litre. How many litres are needed for one coat?
- A circular garden has radius 7 m. Using pi = 3.14, what is its circumference?
- A cylindrical tank has radius 1 m and height 2 m. Using pi = 3, how many litres does it hold when full?
- A taxi charges a fixed fee of 5 reais plus 2.50 reais per kilometre. How much does a 14 km ride cost?
- A bag has 3 red, 5 blue and 2 green balls. One ball is drawn at random. What is the probability that it is NOT red?
- Two fair six-sided dice are rolled. What is the probability that the sum is 7?