Math question please help

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by pemdas » Thu Feb 23, 2012 2:47 pm
nbhardwaj wrote:Suppose you like 1% milk, but you have only 3% whole milk and ½% low fat milk. How much of each should you mix together to make an 8 ounce cup of 1% milk?
two ways to solve this problem - by applying equation or alligation methods. Both shown below

equation method
Let's denote a=3% milk and b=0.5% milk, then Equation 1. 0.03a+0.005b=0.01(a+b) and Equation 2. a+b=8 (ounce cup). Solve for a and b
{30a+5b=10a+10b
{a+b=8

{20a=5b, 4a=b
{a+4a=8, a=8/5 and b=32/5

alligation method
The proportion needed of each starting percentage is the positive difference between the other two percentages.

3% <---> 0.5% // 1%
______________// 8

proportion needed for 0.5% milk = 3-1=2
proportion needed for 3% milk = 1-0.5=0.5

0.5% milk/3% milk=2:0.5=4:1

8 ounce cups will make a whole part of ratios or 5 and the other ratios will be 0.5% milk=4/5 and 3% milk=1/5 OR 0.5% milk=(4/5)*8=32/5 and 3% milk=(1/5)*8=8/5
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by Anurag@Gurome » Thu Feb 23, 2012 8:21 pm
nbhardwaj wrote:Suppose you like 1% milk, but you have only 3% whole milk and ½% low fat milk. How much of each should you mix together to make an 8 ounce cup of 1% milk?
Let us assume that we mix x ounce whole milk, and we mix y ounce low fat milk.
Then x + y = 8 ... Equation 1
3% of x + 1/2% of y = 1% of 8
3x/100 + y/200 = 8/100
3x + y/2 = 8
6x + y = 16 ... Equation 2
Solving equation 1 and 2, we get, 5x = 8 or x = [spoiler]8/5[/spoiler] ounce and y = 8 - 8/5 = [spoiler]32/5 [/spoiler]ounce
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by LalaB » Thu Feb 23, 2012 9:48 pm
it is a weighted average q., and the formula is -

Low milk/whole milk=(3%-1%)/(1%-1/2%)=4:1

low milk =(4/5)*8=32/5

whole milk=(1/5)*8=8/5
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by gmatbeater1989 » Tue Oct 20, 2015 3:19 pm
nbhardwaj wrote:Suppose you like 1% milk, but you have only 3% whole milk and ½% low fat milk. How much of each should you mix together to make an 8 ounce cup of 1% milk?
Can anyone elaborate on using the alligation method for this question?