SAT Math: Geometry

Circle Problem

If the diameter of a circle is 16, what is the area of the circle?

A. 4π
B. 8π
C. 16π
D. 64π
E. 256π

Knowsys Method

Read the question carefully.  Notice that the only information that you have about this circle is the diameter.

Identify the bottom line.  Make a note of the question on your paper: = ?

Assess your options.  You could plug in your answer choices, but you have no reason to do so because you already have the formula for the area of a circle memorized.  The fastest way to get the answer is to use this formula.

Attack the problem.  The area of a circle is equal to pi times the radius squared.  What will you use as the radius?  Remember that the radius is half of the diameter.  The diameter of this circle is 16.  Half of 16 is 8.  That means that your radius is 8.  Now all you have to do is plug the radius into the formula!

Area = πr2
Area = π(8)2
Area = 64π

Loop Back.  You solved for your bottom line, so you are ready to select your answer. 


The answer to this question is (D). 

This is a medium level question. 


Want some help reviewing the math concepts you need to master?  Try out the Knowsys Pre-Algebra Flashcards, the Knowsys Algebra I Flashcards, and the Knowsys SAT & ACT Math Practice book.  

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