Probability of journey times

Hello,

If you assume that the average speed of car will be 30km/hr when making a journey.

A journey distance is 10 km.

You therefore expect the journey to take 20 minutes.

How would you determine how much more likely the journey will take 20 minutes than not to take 20 minutes.

Is it 2, 3, 10 times more likely to take 20 minutes than some other time such as 5 minutes or 35 minutes.

Thanks
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 Recognitions: Gold Member Science Advisor Staff Emeritus You say the "average speed" is 30 km/hr but that alone is not enough information. You need something additional, at minimum the "standard deviation" so that you can at least approximate the probability distribution by a normal distribution.
 okay, thanks. Say for example the SD is 5. How would you determine how much more likely the journey will take 20 minutes than not to take 20 minutes with this extra information included? Thanks for the help