Translation:They run a mile and they run two miles.
comment for the "tips" section of this chapter: the "decimal dot" versus "decimal comma" has to be explained before being used. As given, the numbers there have no sense, and they are confusing. Also, use a different number instead of "1" degree Celsius. Use room temperature, 27°C, or so. Otherwise is confusing and (in physics) false, as 1°C is NOT ~33°F, but it is 1°C=1K= 9⁄5°F= 9⁄5°R (see wikipedia, celsisus, the table at the end of the page).
and in English, "millimeter" is written with double "L" (well, almost always..., and sorry for me being an engineer and a nitpicker in the same time :P)
edit: and try to be constant whenever you use meter or metre (all copy/paste from wikipedia has the right SI unit, metre, but the other text has the American meter (which I also use, unfortunately, in spite of knowing that is not right - well, it actually is not right or wrong, but try to be constant).
I don't see it as weird - even in the UK we use a bastardised mix of Imperial and metric (I have no idea how tall I am in cm nor how much I weigh in stones and lbs, and I am firmly into using Celsius for temperature, but baby birth weight at lbs and oz... go figure). That said, even though I don't use fluid oz in general or Fahrenheit, I still know the term for them, and if I talk to people from, say, the US, I still want to be able to use the correct term for it. They clearly have translations for those measures, so I don't know why it's odd to give both.
Even if in spoken italian language "loro" is used for both subject and complement, the correct grammar has "essi" (m) and "esse" (f) for plural subject, while "loro" should be just complement. Same instance for "lui" and "lei" used as subjects instead of "egli" and "ella". But this will be another course...