Times Greater Than, Times As Much AsDate: 05/02/99 at 01:39:30 From: Kenny Ng Subject: As much as & Greater than I would like to ask you the following questions. 1) A number is five times greater than x. Will this number be 6x or 5x? 2) A number is five times as much as x. Will this number be 5x or 6x? I myself think that the answer to question 1 should be 6x, and the answer to question 2 should be 5x. But my maths teacher disagrees. Can you help me? Date: 05/03/99 at 17:06:19 From: Doctor Peterson Subject: Re: As much as & Greater than Hi, Kenny. Interesting question! I would say that both are 5x, though I see what you are saying, and there are similar phrases where I would definitely say 6x is correct: 3) increased by 500% (not the amount, but the increase, is 500% of the original value.) 4) 500% greater than x (Note that "50% greater than" clearly means "150% of".) 5) 5 times as much again (Likewise, "half as much again" means to add half to what you already have.) These could be called "incremental multiplication," where the multiplication gives not the final number but the amount to be added to the original number. The reason I take (1) as only 5x is that I can't picture using "times" in this way in an incremental sense; I wouldn't say "1/2 times greater." This is why we restrict our use of words in math more than in everyday English (or any other language), to avoid ambiguity, so mathematicians are sometimes seen as being too picky about words. These phrases all really belong to the everyday world, and before we can really do math on them they have to be translated into more proper and careful phrases like "five times x." And I would try to avoid saying "five times greater," because it is definitely on the edge, and might be taken either way. Out of curiosity I just did a quick search for the phrases "times more" and "times greater," and found things like "2.1 times more effective than" in an ad; "100 times more efficient," "10 times more detail," and "60 times more objects" describing telescopes, "100 times faster than" describing a super-computer, and "10 times greater" in an explanation of the Richter scale - the latter clearly is meant to mean "10 times as much," and I think all are intended that way. So if the phrase is correctly interpreted your way, it's certainly so common to misuse it that I would always ask "do you mean 10 times as much?" before doing the math. I also searched the Dr. Math archives, and found one case where a question asks "how many times more likely is it", and the "doctor" quietly rephrases it in his answer, saying "58 times as likely." But in the following answer, the phrase "five and a half times greater" is taken as equivalent to "6 and a half times what it was," agreeing with you (with a warning that "many people don't quite grasp those phrases"). http://mathforum.org/dr.math/problems/zone7.23.97.html So here's my answer: "N times more than X" technically should mean (N+1)X, but is so commonly used to mean NX that it would be dangerous to follow the former interpretation without asking questions. I'm going to keep looking for a dictionary or other authoritative source to support one view or the other (or both, most likely). - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/