How do you define the method of cost per activity?

It is the overall Cost of resources (manpower, equipment , tools) incurred for that activity plus indirect costs which have a certain weightage in that activity as well. 

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Activity based costing ABC is a method for assigning costs to products, services projects, tasks, or acquisitions, based on the activities that go into them and the resources consumed by these activities. ABC contrasts with traditional costing (cost accounting), which sometimes assigns costs using somewhat arbitrary allocation percentages for overhead or the so-called indirect costs.

-      Analog Estimation: This technique relies on the actual cost of previous similar activity as the basis for estimating the cost of the current project activity.

-      Parametric Estimation:uses a statistical relationship between historical and other variables to calculate an estimate for activity parameters, such as cost and budget.

-      Bottom Up estimation: which is the accurate and detailed way, by uploading the resources and materials that will be used for such activity but its inquire a comprehensive activity details.

-      PERT Estimation:When an activity cannot be estimated with a reasonable degree of confidence, the work within the activity is decomposed into more detail. The resource needs are estimated. These estimates are then aggregated into a total quantity for each of the activity’s resources (preferred to be used when the activity is new and has no applied by the company before).