Question 311541
What is the exact area of a circle with a diameter of 19 inches?  
       (a) {{{9.5pi}}} square inches    
       (b) {{{19pi}}} square inches
       (c) {{{38pi}}} square inches
<pre><b>
The formula for the area of a circle is

{{{A=pi*r^2}}} where {{{r}}} represents the radius,

The radius is half the diameter.  Since the diameter is 19,
the radius is half that or {{{19/2}}}

Substituting:

{{{A=pi*r^2}}}
{{{A=pi*(19/2)^2}}}
{{{A=pi*(361/4)}}}
{{{A=(361pi)/4}}} square inches, or as a decimal {{{90.25pi}}}
So it isn't any of the choices you gave.  Maybe you mistyped and 
meant the circumference.  If so, then the formula for the
circumference is 

{{{C=pi*d}}}
{{{C=pi*19}}}
{{{C=19pi}}} inches

So if you meant circumference then that is a choice; however
the unit for circumference is just plain 'inches', not 'square
inches'.  You'll have to ask your teacher what was meant, because
as it is the problem is botched.

Edwin</pre>