help needed with averaging equation

[jonesnich]

I have a large table of data of over/under weights that I need to sort through. The issue is that it is all averaged together even though they need to be weighted differently and I'm not 100% sure how to do this anymore. I have done it in the past, but I don't recall how to do it now. I don't need help with the whole table, I just need help getting started and I think I can figure it out.

Here is a little sample of what I'm dealing with, I'm going to change the name of the variables I deal with to make it a little simpler.
I have 3 types of fish that I caught, catfish, red fish, and bass. I have 233 catfish, 189 red fish, and 171 bass. The weight of the fish that I caught were under the standard of what I was expecting. They averaged out to be -0.12, -0.20, and -0.42 respectively under weight. My table currently averages all of those weights together instead of accounting for how many of each fish there are to affect the weights accordingly. I hope this makes sense... I'm not the best at word problems. Essentially what I need is a formula or for someone to explain what I need to do to get an average of the weights, but I need them to be weighted depending on how many fish there are for each weight.
So if somebody could help me out with this, I would very much appreciate it. Let me know if you need some sort of clarification.
Thanks!

 

[jonesnich]

I have 5 catfish, 4 red fish, and 3 bass. The standard weight for these fish are 4 pounds each. 5 catfish averaged to be 0.5 underweight. 4 red fish averaged to be 0.75 underweight. 3 bass averaged to be 0.25 underweight. The average of all the fish is -0.5. Correct? (-0.5+-0.75+-.25) /3=-0.5
However, this is not the true average of the fish combined. You have -(0.5, 0.5, 0.5, 0.5, 0.5, 0.75, 0.75, 0.75, 0.75, 0.25, 0.25, 0.25). Since there are fewer bass then catfish, this should hurt my overall average, right? I just can't really think of how to ---
I figured it out while explaining it. Thanks Denis!! you're the man!
So you would do 5(-0.5)+4(-0.75)+3(-0.25)/12 fish=-0.52

 

[JeffM]

Sir Jones, thou art smarter than thou thinketh

Really, mon cher denis, if you must tutoyer in early modern English, use the proper "thinkest" rather than the third person form. We are an educational site. I think you have to go stand in the corner of the English teacher.