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To calculate the median number of a set of figures. In this usage, a noun can be used between "average" and "up." You need to average up your expenses and make a budget for yourself. I haven't averaged the kids' test scores up yet, but I don't think it will be a very high number, as most of them failed.
average something up
to calculate the average of a set of figures. Please add these figures and average them up. Please average up all the monthly expenses for the previous year. Will you please average these figures up on the calculator?