The Singing Hedgehog Guide to:
Ratio and Proportion 7

Here is a final example for a popular type of question:

A car travels at 45km/h.
What is this in m/s?

We need to realise that 45km/h means 45 kilometres in 1 hour.
We can now, as usual, write the question as a ratio:

distance : time
45km : 1 hr =
60 mins
work towards the objective of seconds 
work towards the objective of metres45/60km =
0.75km =
 :1 min =
60 secs
divide by 60 to get 1 minute
750/60m =
:1 secdivide by 60 again to get 1 sec

So we find the answer to be 12.5 m/s

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