Substitution/Elimination Word Problems: mixtures

[marissa09]

How do you set these word problems up for substitution/elimination? Each problem will have two equations.

*Low fat milk is 1% milk fat, and whole milk is 4% milk fat. How many ounces of each could you combine to make a 9-ounce mixture of milk with 2% milk fat?

...


*Five hundred gallons of 89 octane gasoline is obtained by mixing 87 octane gasoline with 92 octane gasoline. How much of each must be used?

Help is much appreciated.

 

[galactus]

Re: Substitution/Elimination Word Problems..Help ASAP?

*Low fat milk is 1% milk fat, and whole milk is 4% milk fat. How many ounces of each could you combine to make a 9-ounce mixture of milk with 2% milk fat?

You don't need sub or elimination. We can use one variable.

Let x=the amount of 1%
Then the amount of 4% is 9-x

We have .01x+.04(9-x)=.02(9)

Solve for x

Do the other problem the same way.
...

 

[marissa09]

But then how do you find y so there will be two answers for each problem? Because they both say how many of each.

 

[galactus]

Come on. I stated that x is the amount of 1% and 9-x is the amount of 4%.

 

[stapel]

But then how do you find y so there will be two answers for each problem?

Re-read the set-up and explanation: What is the definition (provided by the tutor) for "the other amount"? If, say, x = 3, then what is the value of "the other"? :wink:

Eliz.

 

[marissa09]

Wow, I feel stupid. Lol. Sorry, I'm tired and stressed out, not really thinking clearly. Thanks a lot.

 

[marissa09]

And now I feel equally stupid because I can't figure out the other equation for the second problem.

Is this right so far?

x = amount of 87 octane gasoline
Amount of 92 octane gasoline is 500-x.

Where do I go from there?

 

[stapel]

Where do I go from there?

Just follow the exact same reasoning and set-up as the first exercise! :wink:

(If necessary, you can review the general process first.)

Eliz.