Question

Which of these is the closest approximation of the area of a circle with a radius of 3.125 cm ?

a.)about 15 cm2

b.)about 30 cm2

c.)about 20 cm2

d.)about 25 cm2

Answer 1

Area = pi times radius squared. 3.125 is roughly 3, and 3 squared is 9. pi is roughly 3, and 9 times 3 is 27. Since you estimated both numbers low, your actual answer will be greater than 27, so B.

Answer 2

its b. the formula is PI * Radius squared. if you do some really rough rounding, PI = 3. now 3.125 is about 3. so using the formula, you do: 3*(3 squared) which is ABOUT 27. now you know that PI is a little bit larger than the number you just used for PI (the estimated of PI), so find a numbr a litle but larger than 27. That is 30.