Not sure how to interpret this

[Aaron6795]

So I have this question
The average result in an exam was 65% with a standard deviation of 5%. There were 200 students in the class. Assuming the results followed a normal distribution, estimate:
a) The percentage of students who achieved results within 1 standard deviation of the mean (above or below)
b) The percentage of students who failed the exam
c)The number of students who got a credit (65%-75%)

I'm not exactly sure where to even start, I understand the formulas to find standard deviation and z scores (if relevant). But all prior work to this hasn't been in percentages or finding deviations in the percentage. Could I please have some guidance?
Thank you in advance

 

[HallsofIvy]

The fact that the numbers are "percentages" is completely irrelevant. You are given a normal distribution with mean 65 and standard deviation 5. For the first problem you don't even have to do any calculations. Just use a table of the standard normal distribution to look up the probability of being between -1 and 1.

The second problem does bother me! It ask for the number of students, out of 200, who fail but doesn't say what a failing grade is.

 

[Aaron6795]

The fact that the numbers are "percentages" is completely irrelevant. You are given a normal distribution with mean 65 and standard deviation 5. For the first problem you don't even have to do any calculations. Just use a table of the standard normal distribution to look up the probability of being between -1 and 1.

The second problem does bother me! It ask for the number of students, out of 200, who fail but doesn't say what a failing grade is.

Sorry I miss typed the second one it does specify less than 50% as the fail grade