Given that diameter of the old circle = 5 cm
Given that diameter of the new circle = 15 cm
Now we have to find the change in circumference from old to new circle.
To find that we need formula of circumference of the circle which is
circumference = D \pi
where D represents diameter of the circle.
Then ratio of the circumference of the both circle is given by
[tex] \frac{Circumference_{old}}{Circumference_{new}}=\frac{D_{old} \pi}{D_{new} \pi} [/tex]
[tex] \frac{Circumference_{old}}{Circumference_{new}}=\frac{5 \pi}{15 \pi} [/tex]
[tex] \frac{Circumference_{old}}{Circumference_{new}}=\frac{1}{3 } [/tex]
That means circumference of the new circle is 3 times more than old circle.
Hence choice "B) multiplies by 3" is correct.
