The best way to look at it is assume there are 60 units of work and the two computers together complete the task in 30 seconds. So together they can do 2 units per second on average. The first computer can do the 60 units of work by itself in 50 seconds, which is 60/50 so it's doing most of the work in the group since the average of the individuals in the group is lower.
I added a picture with it for you. I suggest that before this becomes an issue you take some time and study box and whisker plots, because they tend to show up on a lot of standardized math tests.
