If the circumference of a circle is doubled, the diameter of the circle
(1) remains the same
(2) increases by 2
(3) is multiplied by 4
(4) is doubled
Hello,
you know already that the circumference of a circle is calculated by:
$\displaystyle c=2 \cdot \pi \cdot r= \pi \cdot d$, with diameter = 2 * radius.
Plug in the value you know:
$\displaystyle 12= \pi \cdot d \Longleftrightarrow d=\frac{12}{\pi}$.
In general:
$\displaystyle c=\pi \cdot d \Longrightarrow d=\frac{12}{\pi} \Longrightarrow \pi=\frac{c}{d}$
EB
PS: I've attached a diagram which helps to memorize the right formula: Cover the variable you want to calculate with your fingertip. The remaining term shows how to calculate the covered value.