The cumulative deviation in output is -1.
Here, we are to calculate the cumulative deviation in output using the planned outputs and actual outputs
Actual (A) Forecast (B) Deviation (A-B)
12 10 2
14 15 -1
13 13 0
18 20 -2
Cumulative deviation -1
Therefore, the cumulative deviation in output is -1.
See similar solution here
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