# Standard Deviation Question....Help?

**Incoming students take a mathematics exam consisting of 85 multiple choice questions. Suppose the following is the distribution of the scores on the exam:
Test Score 5-25 25-45 45-65 65-85
Number of Students 20 36 38 6
Find the sample mean score:
a) 41 b) 42 c) 38 d) 37 e) 37.5
The answer is 41 but I cannot figure out how this answer was derived....can somebody please help?
Find the standard deviation:
a) 17.08 b) 17.17 c) 15 d) 292 e) 294.9
Any help would be very much appreciated...please show your work because I have another problem just like this that I need to do on my own...thank you!!!
**

TELL US , if you have any answer