Dec 30 2010 | 7:22 pm

Hello, I'm a max newbie, and I feel like I'm making this problem a lot more complicated than it should be. I've gone through the tutorials on list processing, but I'm still having trouble making progress on this problem.

Given a list (or collection) of the following format:
1 256 0.1
2 128 0.05
3 56 0.03
4 433 0.7

I'd like to calculate a weighted average of the first parameters, using the second parameters as the weights. In other words, I want to take the following steps:
1. Find the reciprocal of the sum of all the second parameters.
2. Multiply each second parameter by this reciprocal.
3. Multiply each first parameter by its corresponding second parameter.
4. Find the mean of the weighted first parameters.

However, I'm already stuck on step 1! I'm not sure how to sum up only the second parameters. Is there an easy way of doing this?