Hello somanyquestionsTo work out (b), it's easiest to use ratios and multiplying factors. If you don't know how to use them, I did a question involving them recently just here.
- Work out the circumference of the tyre in inches.
- Work out how many inches the truck moves forward in 1 hour.
- Divide the second answer by the first; that will tell you how many rotations the tyre needs to make.
The ratio of the radii of the two sets of tyres is . With bigger tyres, the truck will move forward a greater distance for a given number of rotations of the wheels. To find the new distance you will therefore multiply the first one ( miles) by . This tells you how far the truck goes in an hour, and therefore its speed in mph.
So, yes, I think he probably does deserve a ticket.