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# Krisp cereal is 10% sugar by weight. Brano cereal is 2% su

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Manager
Joined: 24 May 2010
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Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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23 Jun 2010, 18:34
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Krisp cereal is 10% sugar by weight. Brano cereal is 2% sugar by weight. If you wanted to make the mixture 4% sugar by weight what should the ratio of Krisp to Brano.
Kaplan GMAT Instructor
Joined: 21 Jun 2010
Posts: 71
Location: Toronto
Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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26 Jun 2010, 17:47
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Krispo is 10%. Bruno is 2%.

Question. Suppose we wanted the final solution to be 6% (not 4%). Because 6 is the midpoint between 10 and 2, wouldn't it then be clear that we would need the final solution to be half of each, and that ratio would be 1:1? It is helpful to visualize this on the number line:

2...6...10

Here we want the final solution to be 4%. So it looks like this:

2.4.....10

Because the grand average is skewed towards Bruno, in order to make the final solution 4%, clearly we need more Bruno than Krisp. In fact, because 4 is only 2 units away from 2 but 6 units away from 10, we need 6:2 or 3:1 as much Bruno as Krisp or 1:3 Krisp to Bruno.

____________

TAKEAWAY: The amount of skew is inversely proportional to the relative quantities of each item. If we have two groups, A, and B, then we have ("x" and "y" represent distance from the total average):

Average of A-------x-------Total average------y--------Average of B

(# in A)/(# in B) = y/x

This concept recurs fairly frequenly on the GMAT, especially in Data Sufficiency questions. If x and y are integers, then using this approach is quick and effective.
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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23 Jun 2010, 19:29
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A similar logic to what I said in the previous question can be used here.

Let us assume he takes x grams of Krisp and y grams of Brano.

So the total weight of the new mixture is (x+y)

Now with respect to percentages, we have:

$$\frac {10}{100}$$ x + $$\frac {2}{100}$$ y = $$\frac {4}{100}$$ (x+y)

So, canceling all the 100s from the denominators, we get

$$10x + 2y = 4(x+y)$$

Rearranging like terms, we get

(10-4) x = (4-2) y

This implies that:

$$\frac {x}{y}$$ = $$\frac {4-2}{10-4}$$ = $$\frac {2}{6}$$= $$\frac {1}{3}$$

Hope this helps.
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Joined: 07 Jun 2010
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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24 Jun 2010, 17:13
whiplash2411 wrote:
A similar logic to what I said in the previous question can be used here.

Let us assume he takes x grams of Krisp and y grams of Brano.

So the total weight of the new mixture is (x+y)

Now with respect to percentages, we have:

$$\frac {10}{100}$$ x + $$\frac {2}{100}$$ y = $$\frac {4}{100}$$ (x+y)

So, canceling all the 100s from the denominators, we get

$$10x + 2y = 4(x+y)$$

Rearranging like terms, we get

(10-4) x = (4-2) y

This implies that:

$$\frac {x}{y}$$ = $$\frac {4-2}{10-4}$$ = $$\frac {2}{6}$$= $$\frac {1}{3}$$

Hope this helps.

it should be

(10y + 2x) (x + y)= 4 (xy)
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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24 Jun 2010, 17:25
Can you explain the logic behind that?
Manager
Joined: 15 Mar 2010
Posts: 78
Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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27 Jun 2010, 20:21
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Jinglander wrote:
Can someone walk me through this please

Krisp cereal is 10% sugar by weight. Brano cereal is 2% sugar by weight. If you wanted to make the mixture 4% sugar by weight what should the ratio of krisp to brano.

An Easier approach:

Attachment:

pic.JPG [ 3.37 KiB | Viewed 6376 times ]

Hence the ratio of quantities is 2:6=1/3
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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28 Jun 2010, 05:23
K -->10
B ---> 2
So 10K+2B = (K+B)4 --> 10K+2B = 4K+4B --> 6K = 2B --> K/B = 2/6 = 1/3
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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09 Apr 2016, 00:42
Jinglander wrote:
Krisp cereal is 10% sugar by weight. Brano cereal is 2% sugar by weight. If you wanted to make the mixture 4% sugar by weight what should the ratio of Krisp to Brano.

Say, w1 is the weight krisp, w2 is the weight of Brano

using weihted average formula w1/w2 = (c2 - avg) / (Avg-c1)

w1/w2 = 4-2 / 10-6 = 2/3

So Krisp and brano should be mixed in the ratio of 1/3.
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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30 Jul 2016, 20:58
.10k+.02b=.04(k+b)
k/b=1/3
Intern
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Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su  [#permalink]

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13 Oct 2017, 04:55
I approached this algebraically:
X= total weight of Krisp
Y= total weight of Bruno

10x/100 + 2y/100=4(x+y)/100
10x/100 + 2y/100=4x/100 + 4y/100
6x/100=2y/100
6x=2y
x=1/3(y)
x/y=1/3
Re: Krisp cereal is 10% sugar by weight. Brano cereal is 2% su &nbs [#permalink] 13 Oct 2017, 04:55
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