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Choclate & Cookie Dough

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by nikhilgmat31 » Mon Aug 10, 2015 4:24 am
Uncle Bruce is baking chocolate chip cookies. He has 36 ounces of dough (with
no chocolate) and 15 ounces of chocolate. How many ounces of chocolate are
left over if he uses all the dough but only wants the cookies to consist of 20%
chocolate?
(A) 3
(B) 6
(C) 7.2
(D) 7.8
(E) 9

Ans is B
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by [email protected] » Mon Aug 10, 2015 9:08 am
Hi nikhilgmat31,

This question can be solved in a couple of different ways. Here's an algebraic approach:

We're told to use 36 ounces of dough and enough chocolate (I'll refer to this amount as X ounces) so that the cookies are 20% CHOCOLATE. This is ultimately a ratio; the information can written in a couple of ways. Here's one...

Chocolate/All = X/(36+X) = 1/5

Now we can solve for X...

5X = 36 + X
4X = 36
X = 9

Thus, 9 ounces of chocolate are needed. Since we started with 15 ounces of chocolate, and the question asks how many ounces are LEFT OVER...

15 - 9 = 6 ounces left over.

Final Answer: B

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Rich
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by Brent@GMATPrepNow » Mon Aug 10, 2015 10:39 am
nikhilgmat31 wrote:Uncle Bruce is baking chocolate chip cookies. He has 36 ounces of dough (with
no chocolate) and 15 ounces of chocolate. How many ounces of chocolate are
left over if he uses all the dough but only wants the cookies to consist of 20%
chocolate?
(A) 3
(B) 6
(C) 7.2
(D) 7.8
(E) 9


Ans is B
We can use equivalent ratios.

The cookies will consist of 20% chocolate.
In other words, the cookies will consist of 1/5 chocolate.
We can also say the cookies will consist of 4/5 dough.

This means the cookies are 4 parts dough and 1 part chocolate.
So, the dough to chocolate ratio = 4/1

We have 36 ounces of dough available.
Let c = the number of ounces of chocolate needed.

We now can use equivalent ratios to set up the equation: 4/1 = 36/c
Solve to get c = 9

So, we need to USE 9 ounces of chocolate, which leave us with 6 ounces REMAINING.
Answer: B

Here's our free video on ratios: https://www.gmatprepnow.com/module/gmat- ... ic?id=1081

Cheers,
Brent
Last edited by Brent@GMATPrepNow on Mon Aug 29, 2016 5:41 am, edited 1 time in total.
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by nikhilgmat31 » Mon Aug 10, 2015 8:40 pm
you got it correct Rich & Brent.

Earlier I was taking X as 20 % of 36

but later realized as X is 20 % of (36 + X)
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