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Discussion in 'Community Discussion' started by Nermal, Jan 26, 2007.
Car A is travelling at 25 km/h. Car B is going 3x faster. How fast is Car B travelling?
Erm... is this a mathematics question or a semantics question? That is, is the active question the difference between "going three times as fast as" and "going three times faster than"?
Typically, at least to an American Engineering-trained mind... the latter phrase should be deprecated.
That is, I typically say:
A is 3x as fast as B -- in this example, 75 km/h
But I don't typically say
A is 3x faster than B
A is 300% faster than B
Because it's never clear if the desired answer is 75 km/h or (what I feel is more technically correct) 100 km/h.
Is this a trick question?
At first guess I would actually say 75 km/hr. Although I guess it could be 100 km/hr as brought up above. Most sane people would say 75 km/hr I believe.
OK, I'll make a fool of myself...
Assuming you mean can B is moving 3x (three times) faster than car A....
25 km/h x 3 = 75 km/h
So car B is moving at 75 km/h.
The answer is D, Not enough information given.
That is what I had initially thought but I'm sure the question wasn't worded correctly.
Ahh.... Of course. I feel so stupid.
You have to tell us the color/s of each car.
Basically I was looking to see whether you guys answered 75 or 100, and I got a mixture of both, which is what I expected.
The reason I bring this up is because Apple uses what I believe to be incorrect notation on their site. For example, the new N AirPort says "5x faster" in some places but "5x the performance" in others; surely 5x faster means 6x the performance.
See, that's my point, though... traditionally, people *do* say things like "A is 100% faster than B" or "A is 50% faster than B." Both of these statements are clearly meant to be interpreted as implying A is faster than B. They are used commonly and almost invariably in this way.
Specifically, for the car B traveling at 25 km/h
A is 100% faster than B is almost always interpreted to mean that A = 50 km/h
A is 50% faster than B is almost always interpreted to mean A = 37.5 km/h
This latter phrase is never interpreted as A = 12.5 km/h.
So it follows that
A is 300% faster than B should mean A = 100 km/h
and the identical statement:
A is 3x faster than B should mean A = 100 km/h as well.
Which, again, is why I avoid saying this. I think most "trained" or formal users of applied math -- engineers, etc. -- will expect you to mean this when you use this kind of terminology. But I agree that how people who are not professionals will make mixed interpretations.
And now that Nermal tipped his hand, I see that's what he was getting at.
I tend to ignore the words following 5x, as that tells me all I need to know: multiply the old result by 5, get new result. The math of 5x is always the same—I prefer not living in some bizarre world where 5 = 6.
EDIT: Well, no, because they're using percentages faster. When someone says 50% faster, they mean 1.5x as fast (since they're essentially saying it's as fast as the original PLUS half that again). I dislike the old "N% faster" terminology, and prefer straight 1.5x, 2.2x, whatever, since then it's always clear what is meant.
300% and 3x are the same by definition... at least to me. I feel that most engineers -- the people who actually design the technology that is 5x as fast as whatever -- would agree with that statement. The key word is the one you ignore -- "faster" vs. "as fast." That's exactly why I'm saying I hate using the 3x or 300% faster than.
Personally, I would have answered "75 km/h".
For the record, if I didn't have any reason to believe that there was something more going on than just a simple question (like, if my nephew had asked me while working on homework, for instance) my answer would have been 75.
The answer is obvious, it is 100.
The only thing obvious is that the answer is not so obvious. Otherwise half the people wouldn't have said 75.
I think we agree, in a roundabout way.
In fact, lemme boil our argument down into something we can both easily agree on:
Stupid ambiguous English!
Are we all so certain that the question is actually grammatically correct in the first place?
No, there is an extra "l" in "traveling".
Besides that, I think it is correct.
From what mkrishnan is saying (I think).
Car B is going 3x faster [than car A].
That means car B's speed equals [(speed of car A + (three times speed of car A)]
no, (as an engineer too), i think
- 300% faster means (as example of 50% faster, means (0.5+1)x) 300%faster aka (3+1)x = 4x
-however when 3x means 3 times of, which implies whatever it is, is 300% of the previous thing.
edit: however the "3x faster" is controdicting because 3x implies 3 "times of", and followed by "faster" which means 3+1 times of
i do agree with you, tho, that the wording is very ambiguous.
Well, the reason many people said 75 is because they arent making the equation in thier head correctly, or i could be wrong....
I just made 25*3+(12.5*2) in my head and got 100, which is the answer to 3x faster.
[because 12.5 is half of 25 and we are adding the number twice more]
100 just came to my mind when i did it in my head, i could be wrong.
But i'm not wrong. i am good at math. ahhh! be more specific in your questions.
enlighten me why you do the 12.5 part?
why is the thread title "A maths question"?
That's what I was wondering when I first saw the thread, heh.
Because we are making it 3x as much, which will require half of the original in each number we add to get our final answer.
Isnt that how *x problems work?
no offend to you, nitynate, but is it just me that has no idea what that means?
when i learend "3x as much" (and that's not even the 3x faster which is very ambiguous).. say a is "3x as much" of b, then a = 3b .. and if b = 25 as in this case, a = 3*25 = 75 (again, i'm talking about 3x as much, not 3x faster in the original post to illustrate how i learnt "3x as much")
but that doesn't involve b/2 anywhere in that equation...