deciphering the DS statement

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ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

by ildude02 » Fri Jun 20, 2008 8:44 am

I was wondering, what we could make out of statement (ii) combined with the question stem.

If on a coordinate plane, point A has the co-ordinates (-3, 4), how far is the point A from point E?

(i) Point E is on the Y- axis four units from the origin.

(ii) If point A were twice as far from point E, it would be the same distance from point E as point C is at co -ordinates (0, -2).

I want to know what we can derive from statement 2? Does it mean, 2 x(distance from A to E) = Distance from A to C? or, can assume the E co-ordinates to be (-3/2, 4/2) as in half the value from the co-ordinates of A(-3, 4) since A is twice as far from point E. I wanted to understand what kind of algebric equation we can make of this statement, if any so it will help me better understand the concept. Appreciate your response.

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Source: Beat The GMAT — Data Sufficiency | Fri Jun 20, 2008 8:44 am

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

Re: deciphering the DS statement

by Ian Stewart » Fri Jun 20, 2008 9:58 am

ildude02 wrote: I want to know what we can derive from statement 2? Does it mean, 2 x(distance from A to E) = Distance from A to C?

Yes, exactly. Since you could, if you wanted to to, find the distance from A to C, you could then divide that by 2 to get the distance from A to E. It's a DS question, so we can skip the calculation, but the information is sufficient.

ildude02 wrote: or, can assume the E co-ordinates to be (-3/2, 4/2) as in half the value from the co-ordinates of A(-3, 4) since A is twice as far from point E.

Here, no, we can't say quite that much. Two things:

-we know E is half as far from A as C is. That does not mean E is positioned midway between A and C; we don't know what direction E is from point A. It might be that E is to the right of A, or below A. All we know is that the distance AE is half the distance AC; we don't know the position of point E.

-also, the midpoint of AC is not at (-3/2, 4/2). To find the midpoint of A and C, average the x and y co-ordinates of A and C: ((-3+0)/2, 4+(-2)/2) = (-3/2, 1).

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

by ildude02 » Fri Jun 20, 2008 10:42 am

Thanks, Ian. I was hoping you would reply since you do the best job of breaking it down.

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