my problem is Let X be a random variable with pmf pk = c/k^2 for k = 1, 2, ....

a.) estimate the value of c numerically.

b) find P[X > 4]

c) find P[6 <= X <= 8]

i'm thinking that i need to do the summation from k=1 to infinite of c/k^2. And i think i can pull out the c and just make it c * the summation of k=1 to infinite of 1/k^2. I then get 1.64493c as the answer for a. I'm not sure what to do for part b or c. any help would be much appreciated.