Using fractions is by far the easiest way to work it out.
Speed is generally expressed as miles per hour. Most of the questions involve distances that are far less than the distance you will travel in one hour. It is far easier to work out the answer when speed is expressed as miles per minute.
90 mph is 90 miles in 60 minutes. 90/60 = 3/2 miles/minute.
So in 2 minutes you will travel 3 miles.
Time = Distance / speed.
Dividing by a fraction is the same as multiplying by its reciprocal. So for example, 12 divided by 3/2 is the same as 12 multiplied by 2/3 (=8).
If you're given a distance and you need to work out the time taken to travel the distance then multiply by the reciprocal.
E.g. Time taken to travel 60 miles at 100 mph?
100 mph = 100/60 = 5/3 = 5 miles in 3 mins.
Time = 60 / (5/3)
= 60 x (3/5) = 36 mins.
By using this method you can quickly work all answers for even the most awkward of speeds. It's just a matter of how well you can multiply and divide. And that takes practice...
With the problem solving exercise, if you have worked out the speeds of all the characters involved before you go to present the solution to the board it can be a big help. Particularly when they throw random questions at you.
If you should end up with fractions of hours, and you need to express things in minutes, it can help to remember that 0.1 of an hour is 6 mins.
If in doubt, just practice your times tables (up to 12). And again... and again... and again... until your maths is slick. How badly to you want to pass OASC?
SBW