Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 04 Jul 2015, 20:36

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# PS: 4 equations/4 variables

Author Message
TAGS:
VP
Joined: 14 May 2006
Posts: 1418
Followers: 4

Kudos [?]: 65 [0], given: 0

PS: 4 equations/4 variables [#permalink]  26 Jul 2006, 16:52
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
guys, this would be probably easy for you, but I can't seem to figure out the fastest approach to solve for any 1st variable. I can easily solve with 2 equations/2 variables, but it takes me a while to figure out equations with more than 2. I understand you must plug-in smaller equations into bigger, but I get all kinds of results that way...

can you show me your methods (fastest) to get one variable?

h+w+d+s=78
h=w+4
d=s+2
h=7s

Thanks.
VP
Joined: 02 Jun 2006
Posts: 1266
Followers: 2

Kudos [?]: 48 [0], given: 0

Here's my method ..

Given
h+w+d+s = 78 ..........(1)

h = w+4 => h-w= 4
d = s+2 => d -s = 2
h-w + d-s = 6
h+w+d+s= 78 .................(1)
2(h+d) = 84 => d+h = 42 ............(2)

Given h = 7s

From d = s+2 => s = d-2
h= 7d - 14 or 7d-h= 14 ....(3)

From (2) & (3):

d+h = 42
7d-h=14
8d = 56

Therefore d = 7.
VP
Joined: 14 May 2006
Posts: 1418
Followers: 4

Kudos [?]: 65 [0], given: 0

haas thanks... makes sense but takes me a bit to do it... will practice this...

do you just start working randomly with equations, or your prefer the ones with only additions first... or the ones that have different variables... or does it even matter?

f.e h=7s and h=w+4... shouldn't be touched because each is solving for h... am I right?
VP
Joined: 02 Jun 2006
Posts: 1266
Followers: 2

Kudos [?]: 48 [0], given: 0

My guideline is to see how many variables can I eliminate at the same time i.e. by a single addition or subtraction operation.

As for not touching an equation, it depends on what variables the eqn involves. In this case h = 7s wasn't necessary to eliminate w and s from the first equation.

In this case adding two simple equations and eliminating the large one makes sense.

My solution was not super quick, but took me less than a minute.. ballpark.

Hope this helps, but then again I am not an expert at Quant... so other experts will probably be more helpful.

u2lover wrote:
haas thanks... makes sense but takes me a bit to do it... will practice this...

do you just start working randomly with equations, or your prefer the ones with only additions first... or the ones that have different variables... or does it even matter?

f.e h=7s and h=w+4... shouldn't be touched because each is solving for h... am I right?
Intern
Joined: 01 Jul 2006
Posts: 18
Followers: 0

Kudos [?]: 0 [0], given: 0

start with variable that touches most of the variables (if that doesn't seem to be obvious, yes , then one could use addition or subtraction between different equation to eliminate most of the variables and be left with one or two)

h+w+d+s=78
h=w+4
d=s+2
h=7s

here s has relation with d and h
so get to put everything in terms of s and see if you can get to one equation.
generally it should i dont expect that GMAT would test our mathematical proving theories than deciphering the eqations.

h = 7s
w= 7s - 4
d= s + 2

7s + 7s - 4 + s + 2 + s = 78
16s = 80
s = 5
h = 35
w = 31
d = 7
VP
Joined: 14 May 2006
Posts: 1418
Followers: 4

Kudos [?]: 65 [0], given: 0

haas_mba07 wrote:
My guideline is to see how many variables can I eliminate at the same time i.e. by a single addition or subtraction operation.

As for not touching an equation, it depends on what variables the eqn involves. In this case h = 7s wasn't necessary to eliminate w and s from the first equation.

In this case adding two simple equations and eliminating the large one makes sense.

My solution was not super quick, but took me less than a minute.. ballpark.

Hope this helps, but then again I am not an expert at Quant... so other experts will probably be more helpful.

u2lover wrote:
haas thanks... makes sense but takes me a bit to do it... will practice this...

do you just start working randomly with equations, or your prefer the ones with only additions first... or the ones that have different variables... or does it even matter?

f.e h=7s and h=w+4... shouldn't be touched because each is solving for h... am I right?

no, no... this is helpful... don't be modest!!! It took me 2.5 min to try to solve it, I still didn't get the answer...
VP
Joined: 14 May 2006
Posts: 1418
Followers: 4

Kudos [?]: 65 [0], given: 0

bondguy wrote:
start with variable that touches most of the variables (if that doesn't seem to be obvious, yes , then one could use addition or subtraction between different equation to eliminate most of the variables and be left with one or two)

h+w+d+s=78
h=w+4
d=s+2
h=7s

here s has relation with d and h
so get to put everything in terms of s and see if you can get to one equation.
generally it should i dont expect that GMAT would test our mathematical proving theories than deciphering the eqations.

h = 7s
w= 7s - 4
d= s + 2

7s + 7s - 4 + s + 2 + s = 78
16s = 80
s = 5
h = 35
w = 31
d = 7

yeah... this is the easiest way I think... very good explanations bondguy, thanks to u 2
SVP
Joined: 30 Mar 2006
Posts: 1737
Followers: 1

Kudos [?]: 46 [0], given: 0

My method.....
Lets convert all into a single in this case lets convert h,d,s into w
Given
h = w+4
7s = h => s = w+4/7
d = s+2 => d = w+4+14/7

Now put it together

w+4 + w + w+4/7 + w+18/7 = 78

=> 16w + 50 = 546
=> w = 31
Intern
Joined: 17 Apr 2006
Posts: 42
Followers: 0

Kudos [?]: 0 [0], given: 0

Select any one variable and isolate it. Take s in this case as it appears on more than one equation

h=7s
d=s+2
w=h-4=7s-4

h+w+d+s = 7s + 7s-4 +s+2 + s = 16s - 2 = 78

therefore: s = 5
Similar topics Replies Last post
Similar
Topics:
4 In the xy plane line m has the equation 4x + y = k. Line n 5 06 Mar 2012, 09:37
I built two 2 variables formulas, which took me 4 min (!) to 6 17 Jan 2008, 05:01
PERMUTATION PS 4 GMAT 10 11 Jan 2006, 05:25
PErmutation 4GMAT PS 4 10 Jan 2006, 17:52
PS-4 7 22 Oct 2005, 19:31
Display posts from previous: Sort by