Answer
$(a)~d=5$ in
$(b)~C=5\pi$ in
Work Step by Step
(a) We know that the diameter relates to the radius by the formula:
$diameter=2*radius$
$d=2r$
We plug in $r=2.5$ in:
$d=2*2.5=5$ in
(b)
We know that the circumference of a circle is given by the formula:
$Circumference=2\pi~radius$
$C=2\pi r$
We plug in $r=2.5$ in:
$C=2\pi~2.5$
$C=5\pi$ in
