Absolute

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 401
Joined: Tue May 24, 2011 1:14 am
Thanked: 37 times
Followed by:5 members

Absolute

by MBA.Aspirant » Sat Jun 25, 2011 4:57 pm
If x is an integer which is less than or equal to |x|, then |-2.4| + |4.4| =

Master | Next Rank: 500 Posts
Posts: 401
Joined: Tue May 24, 2011 1:14 am
Thanked: 37 times
Followed by:5 members

by MBA.Aspirant » Sat Jun 25, 2011 5:56 pm
Is the answer 2+4 or 2.4 +4.4 ?

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2621
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Sat Jun 25, 2011 6:44 pm
MBA.Aspirant wrote:If x is an integer which is less than or equal to |x|, then |-2.4| + |4.4| =
I don't understand the question. What is the point of mentioning x at all here if x isn't part of the expression we need to evaluate?

In any case the absolute value of -2.4 is equal to 2.4, so

|-2.4| + |4.4| = 2.4 + 4.4 = 6.8

edit: I think, in the first part of the question, they are trying to define |x| as the 'floor function' (that is, the function which produces the closest integer to x which is less than or equal to x). If that's the case, the wording is horrible. To avoid confusion with absolute value, we should use a different notation - square brackets, for example. Then if the question were to ask:

For any number x, [x] is defined to be equal to the closest integer to x which is less than or equal to x. What is the value of [-2.4] + [4.4] ?

In that case, [4.4] is equal to 4, and [-2.4] is equal to -3 (and not -2, since it must equal to an integer which is *less* than -2.4), and [-2.4] + [4.4] = -3 + 4 = 1.

But I can't tell what the intention of the question is because the wording and the notation are both ambiguous.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

Master | Next Rank: 500 Posts
Posts: 370
Joined: Sat Jun 11, 2011 8:50 pm
Location: Arlington, MA.
Thanked: 27 times
Followed by:2 members

by winniethepooh » Sun Jun 26, 2011 8:25 am
Awesome explanation Ian, I am your follower now! :wink:

Master | Next Rank: 500 Posts
Posts: 401
Joined: Tue May 24, 2011 1:14 am
Thanked: 37 times
Followed by:5 members

by MBA.Aspirant » Sun Jun 26, 2011 9:56 am
Thanks Ian for your help. The OP had the question exactly as you wrote it, in [x], but when I asked him about it he said it's absolute value. So I'm guessing the original question was talking about the floor function.