It has been some time since my last Stats course and I have what I am sure is a relatively simple problem. My goal is to understand the fundamental difference here.
Take Column A-D. Each row is a new day. Each cell in Columns A and B are independent day to day. Each cell in Column C is equal to A/B. The goal is to provide a Month to Date recording in Column D.
I saw 2 ways of going about this:
Option 1:
for any given cell of $D$, take $D_i = \frac{\sum_{n=A_o}^{A_i}n}{\sum_{m=B_o}^ {B_i}m}$
Option 2: (ignoring the 2nd row with all 0's)
for any given cell of $D$, take $D_i = \frac{\sum_{n=C_o}^{C_i}n}{C_i}$
These give different values however. Option 1 returns a final $D$ value of 13.62% vs Option 2 13.54%.
What fundamental aspect am I missing between this two options. Additionally, which would ideal for the Month to Date value? I'm leaning towards taking the average (Option 2), but would appreciate input.