A multiple choice exam has 10 questions and each question has 5 possible answers. Each question is worth 10 points. If a student taking the exam randomly chooses answers,
a)what is the probability of getting 70?
b)" " 80?
c)" " 90?
d)" " 100?
e)" " >70?

Use the binomial.

The probability of a 70% is C(10,7)(\frac{1}{5})^{7}(\frac{4}{5})^{3}

Do the same for the others.

What if it said, "what is the probability of getting AT LEAST a 70%?".

Then we would sum them up from 7 to 10.

\sum_{k=7}^{10}C(10,k)(\frac{1}{5})^{k}(\frac{4}{5 })^{10-k}

I doubt if you come back anyway, so it probably makes little difference. A large percentage of posters never bother to come back at all after they post their problem.