If a circle whose radius is x has an area of 4 square units, what is t

Question

If a circle whose radius is x has an area of 4 square units, what is the unit area of a circle whose radius is 3x?

(A) 24

(B) 28

(C) 36

(D) 40

(E) 42

Archit3110 · Answer

radius of given circle is 
pi * x^2 = 4
x = 2/√pi
so area of circle with radius 3*x ; 6/√pi
area ; 36 option C

logro · Answer

Given that area of the circle with radius x is 4

Meaning pi*x*x = 4 (pi*x^2)

Now the area of the circle with radius 3x will be

pi*3x*3x = 9pi*x^2

Substituting the above value we get 
The area is 9*4 =36

Hence the OA is C

Posted from my mobile device

rajatchopra1994 · Answer

Explanation:

Area of circle with radius x = π*(x)^2 = 4

Area of circle with radius 3x = π*(3x)^2
= π*(9x^2)
= 9*π*x^2
= 9*4 
= 36

IMO-C

Posted from my mobile device

GMATWhizTeam · Answer

Solution 
 • Area of the circle with radius x  = \pi *x^2 = 4 ........Eq.(i)   square units.

• Also, area of the circle with radius 3x  = \pi*(3x)^2 = 9* \pi*x^2 = 9*4 = 36

Thus, the correct answer is  Option C.

Prep Toolkit