Dear Anna,

 Please consult

https://sites.math.rutgers.edu/~zeilberg/Hist21/q2S.pdf

for the full solutions.


Everything was right except 

In #4 the bottom right numberis 16 NOT 15 (but I did not take points off)


#5:  Essentially the right way, but wrong answer. You took the sum to start at i=0. I took one point off.

You got 9 points (out of 10). 

 Best wishes,

   Dr. Z.