To begin, this isn't "homework" I'm preparing to take a test that will have this types of questions and I wanted to see if I could get any insight and strategies to be able to solve these as quickly and accurately as possible; even mentally if there are any methods (for more complicated types)

So, obviously we've got our formulas:

Distance = Speed * Time

Speed = Distance / Time

Time = Distance / Speed

Also breaking up "chunks of time" in an hour

2 of 30 mins

3 of 20 mins

4 of 15 mins

5 of 12 mins

10 of 6 mins

12 of 5 mins

15 of 4 mins

20 of 3 mins

30 of 2 mins

An example of an easy question to do mentally would be:

Speed of 24 mph, how far would you travel in 1 hour 15 minutes?

0.25 of 24 is 6. Therefore, 24+6 = 30 miles

I'm wondering if anyone knows the quickest most efficient way to solving questions such as:

What speed covers 18 miles in 54 minutes

And if there's a simple way to do it mentally?

I appreciate your replies!

This site has some sample tests including the fuel consumption questions too.

Speed Distance Time | OASC: RAF Officer and Aircrew Selection Centre

Here's a fuel consumption question that I'm wondering what the quickest method to solve would be:

You travel 111 miles. How much fuel will you need if you burn 36 kgs per hour, and are travelling at 148 mph?