C3_W4 exercise 5

In exercise 5 we have to complete a function compute_proportion_metrics. But i don’t understand what I am supposed to code in the x variable.

How do I find the number of users who converted? I could find x by multiplying total people by CVR but the CVR is what we have to find. I don’t understand how or where from I am supposed to extract x?

The hint you need is here:

oh thank you!
but I still don’t understand why would we use that function for x? x is the number of people who converted right? And n is the total number of people, how does the sum of series give us the number of people who converted?

I also do not completely understand why that works. I’ll have to review the assignment. I’ll post back here if I learn anything useful.