In a certain paint store "forest green"

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In a certain paint store "forest green"

by PGMAT » Wed Jun 06, 2012 7:10 pm
In a certain paint store "forest green" is made by mixing 4 parts blue paint with 3 parts of yellow paint. "Verdant green" is made by mixing 4 parts of yellow with 3 parts of blue paint. How many liters of yellow paint must be added to 14 liters of forest green to change it in to "verdant green"?

2
13/6
3
6
14/3

Can some one help me understand how to solve these type of mixture problems?
Source: — Problem Solving |

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by eagleeye » Wed Jun 06, 2012 7:32 pm
Hi PGMAT:

I haven't necessarily seen this type of question before, but this is how I would solve it.

We are given:

For Forest: B/Y = 4/3 or B:Y=4:3
For Verdant: B/Y = 3/4 or B:Y=3:4
We have 14 liters of Forest. Since B and Y are in 4:3 ratio (and 4+3 = 7), we can observe that this solution has 8 liters of B : 6 liters of Y.
Now we need to add x liters of yellow to change ratio from 4:3 to 3:4, so we will have B/(new Y)=3/4
So, 8/(6+x) = 3/4
or, 6+x = 32/3
or, x = 32/3 - 6 = (32-18)/3 = 14/3.

Let me know if this helps :)

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by GMATGuruNY » Thu Jun 07, 2012 2:52 am
PGMAT wrote:In a certain paint store "forest green" is made by mixing 4 parts blue paint with 3 parts of yellow paint. "Verdant green" is made by mixing 4 parts of yellow with 3 parts of blue paint. How many liters of yellow paint must be added to 14 liters of forest green to change it in to "verdant green"?

2
13/6
3
6
14/3
An alternate approach is to work with the ingredient whose volume is NOT CHANGING: in this case, the blue paint.

14 liters of Forest Green:
Since b:y = 4:3 = 8:6, there 8 liters of blue paint.

Verdant Green:
Since y:b = 4:3, of every 7 units, 4 must be yellow and 3 must be blue, implying that the fraction of blue paint = 3/7.
Thus, the 8 liters of blue paint must be 3/7 of the total:
8 = (3/7)x
x = 56/3.

Amount of paint added:
New total - old total = 56/3 - 14 = 56/3 - 42/3 = 14/3.

The correct answer is E.
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