Operations and supply chain: in an inventory management system, which core questions must the system answer to control replenishment and stock levels effectively?

Introduction / Context:
Inventory management systems support purchasing and operations by deciding exactly when to place a replenishment order and how many units to order. These two decisions drive service levels, carrying costs, and stockout risk. Framing the problem correctly separates strategic analysis (e.g., why demand is rising) from operational control (timely reorder decisions).

Given Data / Assumptions:

• An organization tracks on-hand stock, demand, lead time, and costs.
• The system applies policies such as reorder point and order quantity.
• The goal is to maintain availability at minimum total cost.

Concept / Approach:
Classical control focuses on two levers: timing and size. Timing is solved by a reorder point (place an order when inventory position drops to a threshold, often demand during lead time plus safety stock). Size is set by a fixed quantity (like EOQ) or by filling up to a target level (periodic review). Analytics such as ABC classification, service level targets, and safety stock formulas refine these choices, but they still answer the same paired questions.

Step-by-Step Solution:

Verification / Alternative check:
Standard models (EOQ, ROP, periodic review) explicitly compute ROP for timing and EOQ or order-up-to levels for size, confirming these are the primary outputs of an inventory system.

Why Other Options Are Wrong:

• What and why: too general; useful for analysis, not for daily control.
• Who and why: concerns responsibility and rationale, not replenishment math.
• Where and when: location may matter in multi-echelon networks, but the universal pair is timing and quantity.

Common Pitfalls:
Confusing diagnostic questions (why demand changed) with control questions (when/how much). Also, ignoring lead-time variability leads to underestimating safety stock and stockouts.

Final Answer:
when and how much