on or an??

Unpossible

Ok here's the problem;

Today in maths class our teacher started writing the following sentance;

We all know that in average....

Then he stopped and asked me if in is correct (he is finnish), I replied that it should read "on average", then he finished it off with;
300 cars/hour pass a point on the road.

Now as soon as I said "on" another person in class started saying that it should be "an average of", and when we had a fifteen minute break (it was a double class so we got a break halfway) he came over and started arguing about wether it should have been on or an.
Now I reckoned that by putting in a comma and putting the words per hour ( /hour) at the end of the sentance that my verson is correct, I also said that he suggestion might also be used. He insisted that his version was the only correct one.

so can anybody tell me the correct one to use?

The Free Man

we all know that, on average, 300 cars/hour pass a point on the road.
we all know that an average of 300 cars/hour pass a point on the road.

i think they're both right.

Unpossible

yeah, thats what I thought. Like I said though comma's are needed to make my version more grammatically sound. Still, Im interested to hear other opinions.

hullaballoo

Yeah, you don't necessarily need the first comma; it could be written just as accurately, "We all know that on average, 300 cars per hour pass a point". Comma usage is often confused with the use of parentheses, whereby the sentence would be, "We all know that (on average) 300 cars per hour...", and this is due to the fact that the difference in the spoken version is subtle.

For the sake of fluency, you can omit the first comma.

With regard to what your classmate said; "We all know that an average of 300 cars per hour...", I reckon this is also grammatically correct. However, idiomatically, it is obsolete. It's not something that we use commonly in statistical language, which is what we are using when we speak of "averages" and the like. In fact, on second thoughts, I don't think "an average of" can be used at all, but I can't be more specific than to say; it just can't.

PurpleFistMixer

I'd agree with what's been said that they're both correct, but it seems to me that the second one (an average of...) gives a slightly different meaning. It may be just me...
I shall clarify.

We all know that on average, 300 cars per hour pass a point = this would be implying that, generally speaking, there are about 300 cars per hour passing the point, whereas, in the second one,

We all know that an average of 300 cars per hour pass a point = this one sounds more specific, possibly suggesting that it was found out exactly on this road to be an average of 300 cars, maybe earlier on in the question. However, the fact that 'we all know' is there would suggest that the former option, that it's just a general knowledge sort of thing, would be correct.

That may be reading too much into it.

To summarise; that guy who argued with you is wrong.

FlutterinBantam

Good one Fist..... I'm with you on that...... spot on

Victor

we all know that, on average, 300 cars/hour pass a point on the road.

Correct

we all know that an average of 300 cars/hour pass a point on the road.

Poor - not quite on a par with "the bestest best boy", but I would strong ly agree with PFM on this.

An average of 300 cars/hour pass a point on the road.

Correct

Separately, but there are more a matte rfor sentence content than sentence structure:
"a point" should be specified, especially with "an", unless you need to determine the point mathematicly.
"we all know" is open to argument.

FlutterinBantam

You can also do it mathematically