<PRE><B>Question 235351</B>
The surface of a balloon varies directly as the square of its radius.
 The area is  314 sq/cm when the radius is 5 cm.
 What is the area when the radius is 10 cm?
:
If it varies directly as the square, when the radius is doubled the surface area is times 4
4 * 314 = 1256 sq/cm
;
:
You can check this using the surface area formula
S.A = 4*pi*10^2 = 1256.6</PRE>