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GMATT73
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nero44
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GMATT73
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sorry, wrong, let's me try again :oops:
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laxieqv
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nero44
Express the quantities in cookies per camper and set the two scenarios equal.

initial cookies per camper 60/X

if 8 campers dont want cookies, than cookies per camper 60/x-8 + 2

Set those two equal and rearrange... I get to
2x^2 - 16x +240
x^2 - 8x + 240


the method is correct but the equation is x^2-8x-240, Nero! :wink:
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laxieqv
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Matt, there're many ways to solve quadratic equation.
1)Grab a calculator, set mode 1, fill the a, b, c of the quadratic equation into the calcutor, presse enter to get the result.
2) Find delta
3) since the number of campers must be integer .....the expected outcome of the equation must be among the factors of -240 ( including negative factors as well).
Since the equation is quadratic, possibly it has 2 outcomes and the absolute difference of these two outcomes is 8.
the minus sign in front of 8 indicates that the bigger out comes( in absolute value) is negative.
Now, have a glance at 240......such a pairs of outcome is -20 and 12
Then, we can write the equation like this : (x-20) (x+12)=0
easily find out x= 20

The explanation is wordy but in fact , the whole process of reasoning is very quick if you're familiar with this trick :wink:
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nero44
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Agree... method 3) is what I usually use, if excel is not at hand (which certainly isn't the case during the gmat :P)

I guess it depends on how well you are familiar with numbers to see quadratic equations...

else -> PQ or ABC formula.. dont know how you guys call it. its the same thing but I heard different names for it ..
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how do you get x^2-8x-240?

I keep getting +240?

laxieqv
nero44
Express the quantities in cookies per camper and set the two scenarios equal.

initial cookies per camper 60/X

if 8 campers dont want cookies, than cookies per camper 60/x-8 + 2

Set those two equal and rearrange... I get to
2x^2 - 16x +240
x^2 - 8x + 240

the method is correct but the equation is x^2-8x-240, Nero! :wink:
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(60/X)+2=60/(X-8) where X-number of students
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fresinha12
how do you get x^2-8x-240?

I keep getting +240?

laxieqv
nero44
Express the quantities in cookies per camper and set the two scenarios equal.

initial cookies per camper 60/X

if 8 campers dont want cookies, than cookies per camper 60/x-8 + 2

Set those two equal and rearrange... I get to
2x^2 - 16x +240
x^2 - 8x + 240

the method is correct but the equation is x^2-8x-240, Nero! :wink:


The initial portion each gets is : 60/x
After receive 2 more, each receives (60/x)+2
we have : 60/x +2 = 60/(x-8)
Then you get A correct.
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laxieqv
fresinha12
how do you get x^2-8x-240?
I keep getting +240?
laxieqv
nero44
Express the quantities in cookies per camper and set the two scenarios equal.
initial cookies per camper 60/X
if 8 campers dont want cookies, than cookies per camper 60/x-8 + 2
Set those two equal and rearrange... I get to
2x^2 - 16x +240
x^2 - 8x + 240
the method is correct but the equation is x^2-8x-240, Nero! :wink:
The initial portion each gets is : 60/x
After receive 2 more, each receives (60/x)+2
we have : 60/x +2 = 60/(x-8)
Then you get A correct.


laxieqv does everything in a very simple manner...
before:
each camper's share=60/x

after, 8 campers denied cookies:
the no of cookies for 8 campers=8(60/x)
so divide 8(60/x) among the remaining cmpers (x-8) which should equal to 2 = (480/x)/(x-8)

so after simplification, x^2-8x-240=0
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Quote:
how do you get x^2-8x-240?

I keep getting +240?


Here's the step-by-step process:

60/(x-8) = (60/x) + 2
60/(x-8) = (60+2x)/x

cross multiply:

60x = 60x-480+2x^2-16x

the 60x's cancel out, leaving you with:
2x^2 - 16x- 480 = 0

you can divide the equation by two to get:

x^2 - 8x - 240



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