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This is a legal sentence:

London traffic moves at a speed of 11 mph.

Why can't we remove "a" and "of"?

London traffic moves at speed 11 mph.

We may say that "speed" is a variable name and "11" is the value, then a variable name doesn't need an article before as in the question.

Edit: A sentence above is a simplified example (academic writing) for something as:

..X moves at a speed of v..

Edit2: Also we may say that:

a. speed is a variable, because in London a speed is 11 mph, and Paris is 12mph, etc.. .

b. speed is a constant variable with a value 11 mph.

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  • 1
    No, we may not say that. This is English, not physics. We can't remove of because it's necessary for specifying the value, and we can't remove a because it's necessary for specifying the function. Just like you can't remove parentheses and dx's. Jul 18 '21 at 21:34
  • 2
    You can remove "a" and "of" as long as you also remove "speed". Jul 18 '21 at 21:54
  • @JohnLawler, please see my edit.
    – Ben
    Jul 18 '21 at 22:37
  • @KillingTime, I agree ("This is a legal sentence"), but I ask for the reason.
    – Ben
    Jul 18 '21 at 22:47
  • This doesn't seem like a question about English or even Linguistics. Maybe Philosophy?
    – Mitch
    Jul 19 '21 at 3:04
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We may say that "speed" is a variable name and "11" is the value, then a variable name doesn't need an article before as in the question.

But I often see 'the radius r', 'a distance d'.

"The radius 'r'" and 'a distance d' are shortened versions of

"The radius, which, for the sake of brevity, we will call 'r'/which, for convenience, is labelled with the random letter 'r'"

The shortened form is suitable for questions in which the maximum information is conveyed in the minimum words and the literary style is not the paramount concern.

This is not at all the same as "London traffic moves at a speed of 11 mph.", which is (i) quite specific (ii) not a mathematical problem and (iii) the speed is not at all variable - you yourself have stated that it is 11mph.

It is possible to use "at speed 11mph" but only in a mathematical problem, e.g

A lorry has a mass of 20 tonnes. The bend in the road has a radius of 6 metres. At speed 11mph it may safely turn the corner; at speed 12mph it overturns. Calculate its centre of gravity.

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  • please see my edit2
    – Ben
    Jul 18 '21 at 22:42
  • @Ben That's fine. The question still remains "Why can't we say "London traffic moves at speed 11 mph."
    – Greybeard
    Jul 18 '21 at 22:55
  • before or after?
    – Phil Sweet
    Jul 18 '21 at 22:56
  • @PhilSweet :) Good job they were all wearing leathers.
    – Greybeard
    Jul 18 '21 at 23:02
  • Shouldn't the bend in the road also be expressed in miles? :)
    – tchrist
    Jul 18 '21 at 23:27

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