MATH
posted by Anonymous on .
I am working on Measurements and it is one of the most difficult things for me to do. Topics include the SI measurement, Imperial Measurement, and Converting between SI and Imperial Systems.
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.

maybe 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 
That does make a lot of sense, thank you very much Reiny!