## Weighted Average Carrying Cost & Ordering Cost
Sometimes a question asks you to place orders for two (or more) different materials together, where each material has its own carrying cost per unit and ordering cost per order. To apply a single EOQ-style calculation, we collapse the two costs into a single weighted average.
### Weighted Average Carrying Cost
$$\text{Weighted Avg Carry Cost} = \frac{(\text{Units}_A \times \text{Carry Cost p.u. of A}) + (\text{Units}_B \times \text{Carry Cost p.u. of B})}{\text{Units of A} + \text{Units of B}}$$
### Weighted Average Ordering Cost
$$\text{Weighted Avg Ordering Cost} = \frac{(\text{Orders}_A \times \text{Ord. Cost per order of A}) + (\text{Orders}_B \times \text{Ord. Cost per order of B})}{\text{Orders of A} + \text{Orders of B}}$$
### Why we need it
When two materials are bundled into a single purchase order or delivery, costs are shared. A weighted average gives a fair representation per unit/per order, so EOQ logic still applies to the combined order.