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Manager  Joined: 24 May 2010
Posts: 73
Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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8 00:00

Difficulty:   5% (low)

Question Stats: 82% (01:12) correct 18% (01:29) wrong based on 179 sessions

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Kris-P cereal is 10% sugar by weight, whereas healthier but less delicious Bran-0 cereal is 2% sugar by weight. To make a delicious and healthy mixture that is 4% sugar, what should be the ratio of Kris-P cereal to Bran-0 cereal, by weight?

A. 1:3
B. 2:7
C. 2:3
D. 4:5
E. 1:9

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: 64
Location: Toronto
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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8
8
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.
##### General Discussion
Manager  Joined: 15 Mar 2010
Posts: 62
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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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 8807 times ]

Hence the ratio of quantities is 2:6=1/3
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Joined: 09 Jun 2010
Posts: 1808
Concentration: General Management, Nonprofit
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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4
2
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.
Manager  Joined: 26 Feb 2015
Posts: 109
An easy way to find ratios in weighted averages problems  [#permalink]

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1
1
This is a theory I learned through Manhattans Strategy Guides, however, for some reason, they don't always use it in their own problems.

But here goes a quick way to find a ratio. See the following question (taken from Manhattans FDP guide)

"Kris P cereal is 10% sugar by weight, whereas healthier but less delicious Bran-O cereal is 2% sugar by weight. To make a delicious and healthy mixture that is 4% sugar, what should be the ratio of Kris P cereal to Bran-O cereal,by weight?

Instead of setting up a grid, think like this: Kris P is 10%, and 4% is our goal, that means that Kris P is 6 "too much", whereas Bran-O, with its 2% is 2 "too little", which means we need to remove 6 from Kris-P and add 2 from Bran-O

So, x(-6) + y(+2) = 0. In order for this to be 0. X needs to be 2, and Y needs to be 6. Hence, the ratio for Kris P to Bran-O is 2:6 - or 1:3

Hope this helps
Intern  Joined: 07 Jun 2010
Posts: 46
Location: United States
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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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: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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Can you explain the logic behind that?
Intern  Joined: 14 Jul 2009
Posts: 1
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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K -->10
B ---> 2
So 10K+2B = (K+B)4 --> 10K+2B = 4K+4B --> 6K = 2B --> K/B = 2/6 = 1/3
Retired Moderator V
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Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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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: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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.10k+.02b=.04(k+b)
k/b=1/3
Intern  B
Joined: 04 Aug 2017
Posts: 8
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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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
Manager  B
Joined: 01 May 2017
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Location: India
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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10% sugar in Kris-p (x) = 0.1x
2% sugar in Bran-0 (y) = 0.02y
Mixture contains 4% sugar = 0.04(x+y)

0.1x + 0.02y = 0.04(x+y)
0.06x = 0.02y
x/y = 2/6
x/y = 1/3
Math Expert V
Joined: 02 Aug 2009
Posts: 8619
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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Kris-P cereal is 10% sugar by weight, whereas healthier but less delicious Bran-0 cereal is 2% sugar by weight. To make a delicious and healthy mixture that is 4% sugar, what should be the ratio of Kris-P cereal to Bran-0 cereal, by weight?

A) 1:3
B) 2:7
C) 2:3
D) 4:5
E) 1:9

Use weighted average method..
....B0..A.......KP
So 2...4........10
Ratio of KP to B0.....$$\frac{Average-B0}{KP-average}$$=$$\frac{4-2}{10-4}$$=2/6=1/3..

A
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Senior Manager  D
Joined: 15 Feb 2018
Posts: 454
Re: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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What is this "Easier approach" with no explanation posted by achiever01?
Does it have a name? Are there mixture questions where it does not work?
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Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  [#permalink]

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Here is a simple approach: test total weight equals 100 as the weight [b][color=#0000ff]

Thus from the captured table.
0.10x + 0.02(100-x) = 4
0.10x + 2 - 0.02x = 4
0.08x = 2
8x=200
x= 25

Plug back in to find weight of healthy
100-25 = 75
Thus ratio is 25:75 or 1:3
Attachments Capture.JPG [ 36.52 KiB | Viewed 1187 times ]

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Here's how I went from 430 to 710, and how you can do it yourself: Kris-P cereal is 10% sugar by weight, whereas healthier but less delic   [#permalink] 04 Aug 2019, 15:09

# Kris-P cereal is 10% sugar by weight, whereas healthier but less delic  