# Trial & Error Method

A variation of the Repeated Distribution method, used for reciprocal service situations.

## Key Difference from Repeated Distribution

In Repeated Distribution → cost is sent to both production AND service depts at every step.
In Trial & Error → cost is distributed only among service departments in each iteration. Once the service-department totals stabilise (or balances become immaterial), the final stabilised totals are apportioned to production departments in one shot.

## Procedure

1. Start with primary totals of each service department.

2. Apportion S₁ only to other service departments in their ratio (ignoring production departments for now).

3. Apportion S₂ only to other service departments.

4. Keep iterating until service-dept balances are negligible.

5. Then apportion the final accumulated cost of each service department to production departments in the given ratio.

## When to Use

Useful when service-to-service ratios are sharp and iteration converges quickly.
Avoids messy back-and-forth with production-department columns mid-iteration.

Worked example

### Example 1

Example — Trial & Error (logic only):

Primary: S₁=30,000; S₂=20,000.

Inter-service ratios: 30% of S₁ goes to S₂; 30% of S₂ goes to S₁.

Then apportion ₹39,560 (S₁) and ₹31,868 (S₂) to P₁ and P₂ in the production-only ratio.

⚠️ Common exam mistakes

Forgetting the final step — leaving cost stuck in service departments after iterations.
Mixing it up with Repeated Distribution — Trial & Error keeps service depts together until end.
Setting up wrong inter-service ratios (must use only the service-to-service portion of the original ratio).

Reference:

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Trial & Error Method (Reciprocal)

Worked example