Grammar

Economics is written in a mixture of algebra, geometry, and prose. It is easy to see when an algebraic equation or graph is done wrong. The particular attraction of these forms of mathematics and their application in economics is the precision they provide to analysis. To draw a graph with the wrong shaped curves is to get a part of the grammar of the geometry wrong. Everyone in economics expects to have a graph improperly drawn marked off when graded.
Likewise, then with the grammar in our prose. I mentioned that several of the first books I read in economics contained no math whatsoever. Suppose the grammar in those books had been fraught with errors. They would have failed to be convincing. Sloppy graphs, sloppy algebra, and sloppy prose all signal sloppy thinking.
Math is a skill that has to be practiced for proficiency, and writing is the same. It is just as important that your writing be clear as it is that your graphs be drawn correctly, and that your algebra be valid.
The university offers free services to help with writing. You should take advantage of these. You should always, ALWAYS! have at least one other person proofread your work before turning it in.
I will tend to be more lenient on tests and other in-class work, but writing assignments with two week deadlines should be turned in completely error free.