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I want to say that, speed-of-A = (7/4)* speed-of-B. The two sentences that I can think of are:

  1. A runs 7/4 times faster than B.
  2. A runs 7/4 times as fast as B.

I'm told that 1st version is incorrect. I do not understand why. Does it mean speed-of-A = (7/4)(B) + B? I remeber reading sentences like, this processor is 2 times faster than its predecessor. What does faster than actually mean?

  • 1
    From the point of view of language both are of similar meaning, and both are correct. – Man_From_India Jun 2 '15 at 17:02
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    @Man_From_India No, both aren't correct. I am told by someone(here) that 1st version is incorrect. – user31782 Jun 2 '15 at 17:04
  • I believe it has to do with potential ambiguity. Suppose that instead of 7/4 you had 1/2, or 'half' - "A runs half as fast as B" is clear - B is faster, by a factor of 2. "A runs half faster than B" doesn't make sense. It might mean that A is actually 'half-again' (3/2) as fast as B, but it doesn't say that. – MrTheWalrus Jun 2 '15 at 17:04
  • @MrTheWalrus Ok, then we should say 1/2 times slower than. Did I get it right? – user31782 Jun 2 '15 at 17:06
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    @user31782 Oh because that is mathematics. See this link. I knew there is some ambiguity in some speaker's mind, and that's why in my previous comment I mentioned that "from the point of view of language". – Man_From_India Jun 2 '15 at 17:27
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Both of your versions are correct and mean exactly the same thing. The person telling you the first one is wrong is probably thinking of a different circumstance. Suppose instead of "7/4 times" you had said 175%, then you could say "75% faster" but still you would say "175% times as fast" (except nobody actually uses that phrasing, so it would confuse people). And note that your way (either phrasing) is better because it is unambiguous. Anyway, I'd guess that the person saying the first one is wrong is thinking of that circumstance and thinking you should say "3/7 faster" but again, with your inclusion of 'times' that is not the case.

  • Good answer. Native English speakers would not use percentage or fractions with the phrases 'times as fast' or 'times faster'. We say "2 or 3 or 4 etc times as fast/times faster" or "once/twice as fast". Not many people would say "thrice as fast" preferring "3 times as fast". If you want to use percentages, you would say "75% the speed of...". The only time someone would express this as a fraction, would be a very common fraction such as halves and quarters, and even then would probably save "one and three quarters the speed of..." rather then "seven quarters the speed of..." – Steve Ives Jun 3 '15 at 11:43
  • Whoever downvoted this without any comment...that is not how downvotes are supposed to work. You make the downvote to call attention, but you make a comment to point out what you think is wrong. Additionally, you probably should probably make sure of your facts first. FYI, I'm a native (American) English speaker and majored in math...so while of course I could turn out to be wrong--don't bet on it. – elc Jun 3 '15 at 22:40
  • Steve I agree with you that would be weird use of percentages--I was just trying to guess what wrongheadedness could lead anyone to think there was a difference there. – elc Jun 3 '15 at 22:49
  • Well I actually upvoted your answer - you were at -2. – Steve Ives Jun 3 '15 at 23:02
  • Now I am still confused. Some users are saying that 7/4 times faster than is ambiguous and some are saying not. In this question the answer which says times faster can be taken as additive increase is downvoted but here the answers saying the same thing are upvoted. I think that your answer is right because I am finding many references using the times faster than phrasing on corpus.byu.edu/coca , e.g. this [cont]... – user31782 Jun 4 '15 at 15:30
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The first version is ambiguous. In a mathematics course, it would be considered incorrect for this reason.

As you state in your question, the phrase times faster than could be taken to mean a multiplicative increase (A = 1.75B) or an additive increase (A = 1.75B + B).

By using the phrase times as fast as you are eliminating the possibility of the increase being additive by explicitly stating that it is multiplicative.

  • Another unambiguous way to phrase it is, A runs at 175% of B's speed, or A runs at 7/4 times the speed of B, or a variation of this sort. – Damkerng T. Jun 3 '15 at 3:34
  • This is what I thought because when we say x is y amount faster than z then it means x = y + z. I am still confused whether 1st version is ambiguous or not. E.g. In this processor(New) is 2 times faster than its predecessor(Old). What does faster than actually mean? Does it mean speed-of-N = 2*Old or N=3*old? I searched times faster than on corpus.byu.edu/coca it gives many similar sentences, are all these ambiguous? – user31782 Jun 3 '15 at 6:24
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    No native English speaker would ever take the phrase 'times faster than' to be an additive increase. In the example posted, both sentences are correct, although both "seven quarters faster than..." and "seven quarters times as fast..." sound very awkward. However, 'Faster than...' should only be used if the speed is indeed 'faster than' i.e. the speed is greater/the fraction/multiplier is greater than 1. 'As fast as' can always be used e.g. 1/2 as fast as, twice as fast as, 1/10 as fast as etc. – Steve Ives Jun 3 '15 at 11:23
  • You understand the difference between additive (offset) and multiplicative (ratio) just fine. But you are utterly failing at English--and that is really the point here. As a native speaker and a math major, I assure you that "times faster" is the same as "times as fast" and both can only mean multiplicative. – elc Jun 3 '15 at 22:44
  • I do understand that you are thinking that "faster" specifically can only refer to the difference. But for whatever reason, the only time that change is expressed as a ratio is in percentages. (50% faster, 70$ discount, etc) So you can say 100% faster and understand that is the same as 200% as fast. But "one times faster" would just befuddle people. It would be said "two times as fast" (or 'faster'!). I'm not saying that is ideal for mathematical clarity or consistency. It's just how the language is used--and I think what people are looking for here is how to sound polished at English. – elc Jun 3 '15 at 23:19
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  1. A runs 7/4 times faster than B.

Mathematically it means that the difference between A's speed and B's is 7/4 times B's speed, that is A's speed is equal to B's speed plus 7/4 times B's speed. So if we consider B's speed 1 (one unit) then A's speed would be 1+7/4=2.75 units.

Conversely:

  1. A runs 7/4 times as fast as B.

means that the A's speed is 7/4 times B's speed. So if B runs at 1 (one unit) A runs at 1x7/4= 1.75 units.

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    This is not correct.; In English (not in Mathematics) saying that A is x times faster than B means that the speed of A is x times the speed of B. If B's speed is 100m/s, then if A's speed is 2 times faster than B, A's speed is 200 m/s. If A's speed is 3 times faster than B, A's speed is 300m/s. – Steve Ives Jun 3 '15 at 11:26
  • Steve is right and the whole assertion of this answer is wrong. – elc Jun 3 '15 at 22:46
  • This is actually a point where colloquial English is tricky compared to mathematical clarity. The crucial thing here is "times". Let's say A = (3/2) * B. In English, A equals 3/2 times B. It's true that we could also say "A is 50% larger than B" But we could NOT say "A is 1/2 TIMES larger than B" That just sounds nonsensical. Hopefully that makes it clear, when you throw in the "times" you make it clear you are describing the ratio of A to B. Not the ratio of (A-B) to B. But percentanges have some common usages that do cloud things a bit. – elc Jun 3 '15 at 22:59
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The first version is wrong. The second is correct.

If you still want to use "faster than" you could say: A is 75% faster than B.

Or if you insist on fractions: A is 3/4 faster than B.

Note that your first version is akin to 175% faster.

https://math.stackexchange.com/questions/186730/calculate-x-slower-faster

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    Incorrect. Both versions are right in this situation. Because A's speed is greater then B's, you can use 'Faster than'. If A's speed were less than B's, you would not use 'faster than'. Saying "A is 75% faster..." is ambiguous to a native English speaker. Because it sounds wrong (we wouldn't use a percentage here unless in the form "A's speed is 75% of B's speed"), they will ask "Do you mean A's speed is 75% of B's or do you mean it's 175% of B's speed?" – Steve Ives Jun 3 '15 at 11:36
  • @SteveIves I know in my native language kindergartners do it wrong too sometimes, that doesn't make it "all native X speakers" that do it wrong. Seriously, how stupid are you claiming "native English speakers" are? – Jannes Jun 3 '15 at 14:24
  • Saying ten plus ten is 30 is gramatically correct too, but that doesn't mean it makes any sense. Sure, people that don't understand numbers or elementary school math might have difficulty understanding, but there's nothing complex or ambiguous going on here. – Jannes Jun 3 '15 at 16:25
  • @steveives i don't understand why you're accusing me of being hostile or trying to imply that my analogy is me putting words into anyone's mouth. – Jannes Jun 3 '15 at 17:57
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    Jannes the example you link to just says "larger" not "times larger" and that is a crucial difference. But thank you for confirming my theory that the linguistic difficulty here was caused by mistaken application of usages of percentages. Basically the problem with percentages is that sometimes people talk about the ratio A:B and sometimes about (A-B):B and even among native speakers there can be confusion when language is vague--or even when it isn't! – elc Jun 3 '15 at 23:02

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