2 min question again :)

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VP_RedSoxFan: GMAT Instructor; Posts: 85; Joined: Thu May 01, 2008 12:56 pm; Location: Salt Lake City, UT; Thanked: 24 times; GMAT Score:750+

by VP_RedSoxFan » Tue Jun 03, 2008 7:41 am

Not sure I want to get in the middle of this, but, literally, I'm in the middle of this. I consider myself a realist and teach students both methods. Admittedly, I strongly urge students to learn the math, do the math accurately and learn why something is correct mathematically. I really feel that it has the biggest payoff on test day.

However, I'm a realist and will expose my students to backsolving techniques so that on test day, when they're staring at the screen and the algebra escapes them, they have something to lean on. Like Ian, I believe that elite scores go to those who do the math quickly and accurately.

I think it is akin to Sentence Correction questions. Eliminations strategies are better than nothing, but the best scores go to those students with a strong command of grammatical and idiomatic rules.

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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

by Ian Stewart » Tue Jun 03, 2008 9:36 am

VP_RedSoxFan wrote:Not sure I want to get in the middle of this, but, literally, I'm in the middle of this.

Don't mean to start anything serious here(!)- I only hope to have a good-natured discussion of how to best succeed on the test.

VP_RedSoxFan wrote: I consider myself a realist and teach students both methods. Admittedly, I strongly urge students to learn the math, do the math accurately and learn why something is correct mathematically. I really feel that it has the biggest payoff on test day.

However, I'm a realist and will expose my students to backsolving techniques so that on test day, when they're staring at the screen and the algebra escapes them, they have something to lean on. Like Ian, I believe that elite scores go to those who do the math quickly and accurately.

I think it is akin to Sentence Correction questions. Eliminations strategies are better than nothing, but the best scores go to those students with a strong command of grammatical and idiomatic rules.

I think the advice above is the best advice for the GMAT. I teach backsolving as well, but as a fallback strategy, not as a first port of call.

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AleksandrM: Legendary Member; Posts: 566; Joined: Fri Jan 04, 2008 11:01 am; Location: Philadelphia; Thanked: 31 times; GMAT Score:640

by AleksandrM » Tue Jun 03, 2008 9:51 am

Thanks, that is an excellent application of algebra.

https://second-lap.blocked/

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athinabean: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Thu Apr 17, 2008 11:33 am

by athinabean » Wed Jun 04, 2008 9:40 am

area of walkway = (3x+5)^2 - (x+5)^2 = 132

solving we get x = 3

Can somebody please show me how you got x=3 from the above? I cannot do ir for some reason and it is driving me crazy.
thanks.

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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

by Ian Stewart » Wed Jun 04, 2008 10:05 am

athinabean wrote:area of walkway = (3x+5)^2 - (x+5)^2 = 132

solving we get x = 3

Can somebody please show me how you got x=3 from the above? I cannot do ir for some reason and it is driving me crazy.
thanks.

Note that the left side is a difference of squares: a^2 - b^2 = (a+b)(a-b).

So,
(3x+5)^2 - (x+5)^2 = 132

[(3x + 5) + (x + 5)][(3x + 5) - (x + 5)] = 132

(4x + 10)(2x) = 132

8x^2 + 20x = 132

2x^2 + 5x - 33 = 0

(2x + 11)(x - 3) = 0

x = 3, -5.5

Discard the negative solution; distances can't be negative.

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netigen: Legendary Member; Posts: 631; Joined: Mon Feb 18, 2008 11:57 pmFollowed by: 3 members; Thanked: 29 times

by netigen » Wed Jun 04, 2008 10:28 am

BTW roots for the e.q. can be found using the formula

x = [-b+-sqrt(b^2-4ac)]/2a

for an eq of the form ax^2+bx+c = 0

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