help needed! Best way to learn how to set up an equations from a word problems?

[chickenz]

hi,
i've been practicing my gmat for a couple months now. i've already finished kaplan math review and manhattan sc book. my main weakness is math, i seem to have a lot of trouble setting up and equation out of a word problem..i understand the terminology very well..like in addition to, or less than. (+, -)
but it is setting up an algebraic equation to solve a simple problem that throws me off.

for example: a rabbit on a controlled diet is fed daily 300 grams of mixture of two foods, food X and food Y. Food X contains 10% protein and food Y contains 15% protein. if the rabbit's diet provides exactly 38 grams of protein daily, how many grams of food x are in the mixture.

this doesn't seem like a really difficult problem...but now i'm stuck when trying to set it up.

the answer sets the problem up as follows:
.10x + .15(300-x) = 38
x=140


i;m having such a hard time coming up withe .10x + .15x(300-x) = 38 part..i understand the reason behind it after i read the explaination..and if a problem that comes up that looks similar to this one i probaly could solve it again..but of course the gmat isn't like that..every problem changes..so once again i get stuck!

any suggestions on how to get better at this? ..i bet if i can learn how to set these up i would get a higher score
thanks

[GREMAT]

chickenz,
the best way is to practice a lot and analyze the solutions provided by others.
Search posts by GMAT-HELP, he is a wizard for translating word problems to math terms.

[chickenz]

thanks for your advice..i will look up some of his or her posts now!