This question's explanation and your answers so far.
表は，シュウマイ弁当の原材料表の一部である。100個のシュウマイ弁当を製造するために必要な豚肉の量は何グラムか。ここで，このシュウマイ弁当にはシュウマイ以外に豚肉を使う料理は入っていないものとし，製造過程での原材料のロスはないものとする。
| 製造品 | 製造量 | 製造量単位 | 原材料 | 原材料量 | 原材料量単位 |
|---|---|---|---|---|---|
| シュウマイ弁当 | 1 | 個 | シュウマイ | 5 | 個 |
| 白飯 | 300 | グラム | |||
| ... | |||||
| シュウマイ | 1 | 個 | シュウマイの皮 | 1 | 枚 |
| シュウマイの具 | 20 | グラム | |||
| ... | |||||
| シュウマイの具 | 100 | グラム | 豚肉 | 60 | グラム |
| 玉ねぎ | 30 | グラム | |||
| ... | |||||
| ... |
1,200 is the error of forgetting the level where each bento contains 5 shumai, computing 100 bentos × 20 grams of filling × 0.6 = 1,200. In reality each bento contains 5 shumai, so it must be multiplied by a further 5.
3,000 is the value obtained by calculating with the ratio of 30 grams of onion instead of 60 grams of pork (10,000 grams of filling × 30 ÷ 100 = 3,000). The question asks for the amount of pork, so this mistakes which ingredient amount to reference.
正解 This table is a bill-of-materials (BOM) style ingredient list that shows, level by level, “which ingredients and how many of each are needed to make one product”. Multiply the quantities from the top level downward to obtain the required amount. First, 100 bentos each contain 5 shumai, so 100×5=500 shumai are needed. Each shumai contains 20 grams of filling, so 500×20=10,000 grams of filling are needed. From the bottom row, the filling contains “60 grams of pork per 100 grams” (i.e., pork is 60 percent of the filling), so the pork is 10,000×(60÷100)=6,000 grams. Therefore the correct answer is ウ, “6,000”.
30,000 is the error of ignoring the filling-to-pork conversion of “60 grams of pork per 100 grams of filling” and directly multiplying 500 shumai by 60 grams of pork (500×60=30,000). Each shumai has only 20 grams of filling, which yields no more than 12 grams of pork.