Final answer:
Flexible budget variances occur due to differences in standard and actual per-unit amounts.
Step-by-step explanation:
The missing term in the given question is actual. Flexible budget variances occur due to differences in standard and actual per-unit amounts.
Flexible budget variances are the differences between actual and standard costs. The standard cost represents the planned or expected cost per unit, while the actual cost represents the cost that was actually incurred. By comparing the standard cost and the actual cost per unit, we can calculate the flexible budget variance.
For example, if the standard cost per unit is $5 and the actual cost per unit is $6, the flexible budget variance would be $1. This variance could be due to various factors such as changes in the cost of inputs or inefficiencies in the production process.