If I have an 101 A in my math class and I get a 70/100 (Which is a D), what grade will I have in that class?
This is a difficult question to answer without more information. Are the test weighted equally? Does the teacher grade based on improvement? Without more information, it will be hard to know your grade for certain.
If both tests are weighted equally, then you have an numerical average of 85.5. In most schools this is a B. But what you should do is to see your school's grading distribution to know for a fact.
If the one of the grades (for example, the 101) was a test grade and the other grade was a quiz grade, then your average will probably be higher than the 85.5. However, if the 101 grade was a small quiz and your 70 was a major test, then your grade will be lower than 85.5. So, what you will need to know is how each test is weighted.