The Solution:
It is given in the question that the ratio of the diameter of the front wheel of a penny-farthing to the diameter of the back wheel is 13:4
[tex]\begin{gathered} \frac{D}{d}=\frac{13}{4} \\ \text{Where} \\ D=\text{diameter of the front wheel} \\ d=\text{diameter of the back wheel} \end{gathered}[/tex]We are required to find the ratio of the circumference of the front wheel to the circumference of the back wheel.
Step 1:
The formula for the circumference of a wheel (that is, a circle) is
[tex]\text{ circumference of a wheel = 2}\pi r=\pi d[/tex]Step 2:
We shall find the ratio of the circumference of the front wheel to the circumference of the back wheel.
[tex]\begin{gathered} \frac{\pi D}{\pi d}=\frac{13\pi}{4\pi}=\frac{13}{4} \\ \text{ So,} \\ 13\colon4 \end{gathered}[/tex]Therefore, the required ratio is 13:4