Question

Which of the following speed units is NOT from the Si (metric) system?*

cm/s
m/min
km/hr
mi/hr
m/s
km/min

Answer 1

Prefixes are not usually used to indicate multiples of a second greater than 1; the non-SI units of minute, hour and day are used instead. On the other hand, prefixes are used for multiples of the non-SI unit of volume, the litre (l, L) such as millilitres (ml).