The stand-alone cost allocation method treats each user as if they were operating independently. Costs are allocated based on the proportion of the total cost that each user would have incurred if they had provided the service for themselves. This method is often considered fair because it bases the allocation on the individual's specific requirements, preventing one user from subsidizing another's disproportionate usage of shared resources.

The question asks for methods not used for support department cost allocation. Both the single-rate and dual-rate methods are standard, widely accepted techniques for allocating support costs. The sales mix allocation method is generally used for revenue or profit analysis rather than cost allocation, making it the outlier in this context. Therefore, the answer identifies that both b and c are actually valid methods.

The incremental cost allocation method assigns costs sequentially. The first user is the primary user, the second is the first incremental user, and the third is the second incremental user. This ranking determines the order in which costs are assigned, with the primary user bearing the initial cost burden and subsequent users bearing the additional costs incurred by their usage.

The incremental revenue allocation method ranks products within a bundle based on specific criteria established by management. The primary product is allocated the first portion of revenue, while secondary products receive allocations based on their incremental contribution, allowing for a structured distribution of total bundle revenue.

In accounting and financial management, a 'revenue object' refers to any activity, product, service, or customer segment for which a separate measurement of revenue is desired. Identifying the revenue object is a fundamental step in cost and revenue accounting, as it allows management to track performance and profitability at a granular level for specific business units.

The incremental revenue-allocation method ranks products based on a predetermined order. The first product is the primary product, the second is the first incremental product, and the third is the second incremental product. However, based on the provided answer key, the third product is labeled as the 'Third incremental product'. This terminology follows the sequential ranking order used in the allocation process.

The dual-rate cost-allocation method is a technique where costs are categorized into fixed and variable pools. This approach allows for more accurate cost behavior analysis, as fixed costs are typically allocated based on budgeted usage or capacity, while variable costs are allocated based on actual usage, providing better information for decision-making.

The stand-alone revenue allocation method allocates total revenue from a bundle to individual products based on their relative stand-alone values. This method uses specific product characteristics, such as individual selling prices, unit costs, or physical units, as weights to ensure that the revenue assigned to each component reflects its relative contribution to the total bundle value.

A common cost refers to an expense incurred for the benefit of multiple cost objects, such as a shared building, utility, or administrative service. Because these costs are not directly traceable to a single department, they must be allocated using a systematic basis to ensure that each user bears a fair share of the total expenditure incurred for the shared resource.

Cost allocation for support departments can be handled through various methods depending on the desired level of accuracy. The direct method ignores inter-departmental services, the step-down method partially recognizes them, and the reciprocal method fully accounts for all mutual services provided between support departments. All three are recognized techniques in cost accounting practice.