問23
頻出度★★☆
1個の製品Aは3個の部品Bと2個の部品Cで構成されている。ある期間の生産計画において，製品Aの需要量が10個であるとき，部品Bの正味所要量（総所要量から引当可能在庫量を差し引いたもの）は何個か。ここで，部品Bの在庫残が5個あり，ほかの在庫残，仕掛残，注文残，引当残などは考えないものとする。
平成21年度 春期 ITパスポート試験 問23
This question's explanation and your answers so far.
解説
問 23
Incorrectア
20 is the gross requirement for “part C”, which is needed at 2 units per product A (2 × 10 = 20 units); it is not the value for part B, which is what the question asks about. It is an easy wrong choice to pick if you mix up the per-unit quantities of part B and part C (3 units and 2 units).
- イ
正解 The net requirement is obtained as “gross requirement − allocatable on-hand stock”. First find the gross requirement. Each product A needs 3 parts B, and the demand for product A is 10 units, so the gross requirement for part B is 3 × 10 = 30 units. Next, subtract the allocatable on-hand stock. Part B has an on-hand stock balance of 5 units, and other stock balances, work-in-process balances, on-order balances and allocated balances are not considered, so the allocatable on-hand stock is simply 5 units. Therefore the net requirement is 30 − 5 = 25 units, and イ is correct. Note that part C (2 units per product A) is not what the question asks about, so it plays no part at all in this calculation.
Incorrectウ
30 is exactly the “gross requirement” for part B (3 × 10) itself, with the on-hand stock balance of 5 units not yet subtracted. The net requirement is the gross requirement minus the allocatable on-hand stock, so leaving it at 30 does not satisfy that definition.
Incorrectエ
45 comes from lumping part B and part C together without distinguishing them, giving a requirement of (3 + 2) × 10 = 50 units, and then subtracting the on-hand stock balance of 5 units. This ignores the basic practice of bill of materials (BOM) explosion, in which requirements are calculated separately for each part, and on top of that it mixes the requirement for part C into part B.
ここがポイント
- The basic MRP (Material Requirements Planning) formula: net requirement = gross requirement − allocatable on-hand stock. Do not answer with the gross requirement as it is; always subtract the on-hand stock.
- Gross requirement = demand for the parent item × the quantity per unit on the bill of materials (BOM). Requirements are exploded separately for each part; do not mix in another part's per-unit quantity.
用語