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Tips and Tricks: Mixtures

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Tips and Tricks: Mixtures [#permalink]

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New post 30 Apr 2013, 14:45
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Hi guys!

This is my second post of Tips and Tricks, if you have missed the first one be sure to check it out :arrow: Inequalities

In this one I will show you a method (disclamer: I did not invente it :roll: ) to solve easly any mixture problem: it's called Alligation.

It uses a simple table to solve any mixture problem, every answer to such problems can be obtain by looking at this table .

Attachment:
alli.png
alli.png [ 6.15 KiB | Viewed 16638 times ]

Please note: the X concentration is the highest, the Y is the lowest

The results that you get by subtracting, as I show you in the table, are the ratios of the substances in the desired mixture.
\(RATIO\frac{X}{Y}=\frac{Desired-Y}{X-Desired}\)

An exmple will explain better than any of my words because this method is really simple to use. I took the following questions from here if you want to get some practice you can try some of those.

1)Seed mixture X is 40 percent ryegrass and 60 percent bluegrass by weight; seed mixture Y is 25 percent ryegrass and 75 percent fescue.
If a mixture of X and Y contains 30 percent ryegrass, what percent of the weight of this mixture is X ?
(A) 10%
(B) 33.33 %
(C) 40%
(D) 50%
(E) 66.66 %

The question asks for the ryegrass so your table should look like this:
Attachment:
all1.png
all1.png [ 2.28 KiB | Viewed 16649 times ]

Solution: The final raio is\(\frac{X}{Y}=\frac{5}{10}\) (or \(\frac{1}{2}\)) so for every 1 part of X 2 parts of Y will be in the final mixture
So for a 3 kg mixture (for example)=> 1X and 2Y => \(X=33%\) of the total B

This table can be used in other ways also, and this question is an example:
2)How many liters of pure alcohol must be added to a 100-liter solution that is 20 percent alcohol in order to produce a solution that is 25 percent alcohol?
(A) 7/2
(B) 5
(C) 20/3
(D) 8
(E) 39/4

Your table:
Attachment:
all2.png
all2.png [ 2.4 KiB | Viewed 16605 times ]

Final ratio: \(\frac{X}{Y} = \frac{5}{75}\)
We know that Y is 100 liter so \(\frac{X}{100}=\frac{5}{75}\) \(X=\frac{20}{3}\) C
Easy!

As you see mixture problems start to look very easy if you consider this method, and for sure all this will save you valuable time 8-)
Hope you guys like it

Cheers
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Re: Tips and Tricks: Mixtures [#permalink]

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New post 02 May 2013, 18:03
Zarrolou-- thanks for showing some new approach !
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Re: Tips and Tricks: Mixtures [#permalink]

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New post 29 Jun 2014, 07:32
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Re: Tips and Tricks: Mixtures [#permalink]

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New post 08 Dec 2014, 13:18
Zarrolou- Thanks for the approachThree grades of milk are 1 percent, 2 percent and 3 percent fat by volume. If x gallons of the 1 percent grade, y gallons of the 2 percent grade, and z gallons of the 3 percent grade are mixed to give x+y+z gallons of a 1.5 percent grade, what is x in terms of y and z?

A. y + 3z
B. (y +z) / 4
C. 2y + 3z
D. 3y + z
E. 3y + 4.5z

Can you please let me know how I could solve this question with the help of your table.
Basically I need the table for more than 2 unknown mixtures.
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Re: Tips and Tricks: Mixtures [#permalink]

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New post 08 Dec 2014, 13:20
Expert's post
sagarswamy wrote:
Zarrolou- Thanks for the approachThree grades of milk are 1 percent, 2 percent and 3 percent fat by volume. If x gallons of the 1 percent grade, y gallons of the 2 percent grade, and z gallons of the 3 percent grade are mixed to give x+y+z gallons of a 1.5 percent grade, what is x in terms of y and z?

A. y + 3z
B. (y +z) / 4
C. 2y + 3z
D. 3y + z
E. 3y + 4.5z

Can you please let me know how I could solve this question with the help of your table.
Basically I need the table for more than 2 unknown mixtures.


You can check various methods to solve this question here: three-grades-of-milk-are-1-percent-2-percent-and-3-percent-fat-126122.html

Hope it helps.
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Re: Tips and Tricks: Mixtures [#permalink]

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New post 17 Mar 2016, 11:13
Hello from the GMAT Club BumpBot!

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Re: Tips and Tricks: Mixtures [#permalink]

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New post 03 May 2016, 01:46
Wow, this makes mixture problems so much easier. That's one of the sections i've been having problems understanding the logic behind them.
First i think i need to look at these graphs to get used to using this method, but after a while i think it will just pop from the back of my head.
THAnK YOU!
Re: Tips and Tricks: Mixtures   [#permalink] 03 May 2016, 01:46
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