Can you add multiple duration fields in a single record to get a 'total' duration?

I have a table with a series of counts that are entered for different tasks. Each task 'should' take a certain number of minutes. For each task, I have the count (entered by user), the average number of minutes it should take to perform, and a duration formula that multiplies the count by the avg min. I need to sum this 'duration' for a series of tasks so that I can get a total duration for all tasks in this record.