In collegelevel math courses, a D is equivalent to an F. Why?
Can be used to get into next course? Can be used as a prerequisite for a nonmath course? Can be used to transfer?  D No No No  F No No No 
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In collegelevel math courses, a D is equivalent to an F. Why?
It is incredibly important that you realize your grade is not only dependent on your level of knowledge. Unfortunately, it is also a function of your instructor's grading scheme and rigor level. Some instructors are extremely tight with their grades while others pass almost every student and give half the class B’s or A’s (in spite of the student’s true knowledge).
As of this moment, if you have a C in the prerequisite math course, you are allowed to take the next course in the math sequence. This forces the instructor to hold a tight rigor level on passing versus not passing. The instructor must ask themselves, "Does this student know a decent amount of the material and will they stand a fair chance at surviving in the next math course?"
The C = 70% line is somewhat arbitrary and changes from country to country. Some countries consider “acceptable” knowledge to be 60% while others consider it to be 80%. More on this in the next paragraph.
In quickanddirty terms, grades exist as a means for academia to measure your knowledge base and determine when you're ready to move to “the next level.”
