Answer:
C. 66.4 mph
Step-by-step explanation:
∵ The ratio of speed of motorcycle and the circumference of the tyre is constant for a motorcycle,
If x be the speed ( in mph ) of a motorcycle having the tyre of diameter 28 inches,
⇒ The ratio of speed and circumference = \frac{x}{2\pi (14)}
( Because radius = Diameter / 2 ),
While, the speed of the same motorcycle having the tyre of diameter 25 inches is 60 mph,
⇒ The ratio of speed and circumference = \frac{60}{2\pi (12.5)}
By the above statement,
\frac{x}{2\pi (14)}=\frac{60}{2\pi (12.5)}
\implies x=\frac{60\times 14}{12.5}=\frac{336}{5}=67.2\approx 67
So, the actual speed of the motorcycle after changing the tyre is 67 mph ( approx )
Hence, option 'C' is correct.
Step-by-step explanation:
