Answer:
multiply by km/mi = 1.609344 (exactly); about 8/5
Step-by-step explanation:
Let "cf" represent the conversion factor we wish to multiply by. Then the units of the conversion factor can be found from ...
km/h = cf · mi/h
Multiply this by h/mi and you get
(km/h)·(h/mi) = cf
km/mi = cf
In order to have this multiplier have a magnitude of 1, the numerator distance must be equal to the denominator distance. So, you need to know the number of kilometers in 1 mile. You can find that several ways, but perhaps the easiest is to look it up on the Internet. There are 1.609344 kilometers in 1 mile, so the conversion factor to multiply by is ...
(1.609344 km)/(1 mi)
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For estimating purposes, it may be convenient to use the factor 8/5, which is within 0.6% of the correct value.
Then 75 mph is 1.609344×75 kph = 120.7008 kph
