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December 20, 2014

December 20, 2014

Posted by **Anonymous** on Wednesday, September 15, 2010 at 7:18pm.

I would like to do some review on this and would like to know a easier way to all problems.

Montgomery ran 100m in 9.78s. What was the runner's speed in kilometres per hour?

How do I do this? Do I convert metres to kilometres first? How do I convert seconds to hours? I just don't get it . Can someone please provide me with clarification.

- MATH -
**Reiny**, Wednesday, September 15, 2010 at 7:38pmmaybe this will make sense to you .....

100 m = .1 km

and 1 sec = 1/(60x60) or 1/3600 hour

so 100 m/9.78 sec

= .1 km/(9.78 x 1/3600) hr

= 36.8 km/hr

or look at it this way ...

there are 3600 seconds in 1 hour.

so by dividing 3600 by 9.78 we would get 368 legs of 100 m, but 10 of those 100 stretches make 1 km, so divide 368 by 10 to find the number of km

or 36.8 km/hr

I would simply form a ratio using the same units the same units

.1 km/9.78 sec = xkm/3600 sec

cross multiply

9.78x = .1(3600)

x = 360/9.78

x = 36.8

so x = 36.8 km/3600 sec

= 36.8 km/hr

- MATH -
**Anonymous**, Wednesday, September 15, 2010 at 8:02pmThat does make a lot of sense, thank you very much Reiny!

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