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How to calculate speed in min/km given distance in meters and time seconds? I used formula v = d/tbut having problems converting units.

I've tried ((distance_m/1000) / (time_sec/60)) and got something ~ 0.2 and I'm expecting something around 4:08 min/km

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  • $\begingroup$ Can you elaborate on what you have tried? $\endgroup$ – ZeroTheHero Aug 15 '17 at 15:55
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    $\begingroup$ Speed is in distance per time, not time per distance. Have you tried multiplying by one? $\endgroup$ – user121330 Aug 15 '17 at 16:01
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Unit conversions are an important part of any science. Usually, to convert from one unit to another, you can just multiply by one or more conversion factors.

For example, to get ${min\over km}$ from ${m\over s}$ you convert $s$ to $min$ by the factor of $60 s\over 1 min$ and $m$ to $km$ by the factor of $1000 m \over 1 km$. To use the factors properly, flip them so that the units cancel properly. $$x{m\over s} * {60s\over 1min} * {1 km\over 1000 m} = x{60 km\over 1000 min}$$

Now we can convert $x {m \over s}$ to ${km \over min}$ by multiplying $x$ by our conversion factor. If you want to get $min \over km$ instead of $km \over min$, then simply invert the fraction: $$x{km\over min} \to {1\over x}{min\over km}$$

This process of using conversion factors allows you to express any value in terms of nearly any unit. I say "nearly" because some units can't convert (for example, you can't normally express temperature in terms of speed, that wouldn't make sense in just about any context).

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How many seconds are in a minute? Every second is equal to...?

How many metres are in a kilometre? Every metre is equal to...?

The part where you're most likely to go wrong is whether to multiply or divide to go from second to minute or metre to kilometre. Just remember that if the unit at the end denotes something bigger (e.g kilogram is bigger than a gram) there is going to be less of it at the end of your calculation.

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protected by Qmechanic Aug 15 '17 at 17:48

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