Interviewer instructions
Days of inventory of main input. The purpose of this question is to assess the efficiency in the supply chain. When firms have to maintain a high level of stock, because they cannot rely on a predictable supply of inputs, this is a source of economic inefficiency. Inversely, if supplies of the main input can be relied upon to be easily available, firms will keep low levels of stock on hand.
The main input is the input that accounts for the highest value among all inputs. It is not the input for which stock is maintained the longest. For example, if a company makes shirts, the most important input is the cloth, not the buttons and thread, though the establishment may actually keep a 90 day supply of buttons on hand and only a 30 day stock of cloth.
Days of inventory should be calculated as the number of days of normal production capacity before running out of stock.