System boundaries and resource flows Review questions System boundaries and resource flows A crate balance reconciles opening stock and purchases with ending serviceable, damaged, customer-held and confirmed lost units; a customer-held asset is not waste. Dispatch and receipt require identifiers and a shared cut-off to avoid fictional loss from reporting periods. For single-use versus durable packaging, equal service and achieved lifetime matter more than item weight. New durable material equals required services divided by actual cycles times unit mass. One batch’s return rate is not complete lifespan, and mass does not settle washing or transport. When warehouse, carrier and customer ledgers conflict, keep the gap pending, assign its evidence owner and recommend a reversible test before permanent purchasing.
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Question 1 In the Jeddah case, opening stock is 1,200, purchases are 300, dispatches 900, and returns comprise 700 serviceable and 80 damaged; 80 remain with customers and 40 are lost. What is ending physical serviceable stock? 1,300 crates: subtract dispatches and add only serviceable returns. 1,380 crates: add damaged returns to serviceable stock. 1,420 crates: add all non-returned crates to warehouse stock. Question 2 For 1,200 deliveries, compare a 20-gram single-use container with a 200-gram durable one achieving ten actual cycles. What is the new-packaging mass result? Single use 24 kg, durable 2.4 kg, by dividing mass by cycles twice. Both use 24 kg of new packaging at ten cycles. Single use 240 kg and durable 24 kg because delivery count directly gives kilograms. Question 3 A centre lists 400 crates prepared, ten remain onsite, and the carrier scans 390 exits. A customer confirms 380 before cut-off and ten afterward with matching identifiers. What remains unexplained? Zero: 390 left and 390 were received across two periods. Ten: anything after cut-off is permanently lost. Twenty: subtract in-period receipts from preparation without reconciliation. Question 4 A cafeteria prepared 540 meals and served 475. It cuts preparation to 510, demand remains 475 and standby production is unused. What is the new surplus? 35 meals, while demand-service performance still needs checking. 65 meals because demand is unchanged. Zero because lower preparation prevents all surplus. Question 5 Repairing 40 devices costs 120 each and 30 pass. What is repair cost per accepted device before transport and downtime? 120 because failed attempts do not belong in success cost. 144 by adding the 30/40 success ratio to repair price. 160 because all 4,800 spent on attempts are divided by 30 accepted. Question 6 An 800-kg stream has 400 kg organic at 75% acceptance, 250 kg packaging at 40%, and 150 kg contaminants rejected. How much is accepted? 650 kg by adding all organics and packaging before acceptance. 400 kg: 300 organic and 100 packaging. 800 kg because all entered sorting. Question 7 For 1,800 equal services, single-use boxes weigh 24 g; durable boxes weigh 240 g and achieve 15 cycles. What new-packaging mass is needed? Both require 43.2 kg simply because service is equivalent. Single use 43.2 kg and durable 28.8 kg before washing and transport. Single use 24 kg and durable 240 kg because item weight is the denominator. Question 8 New manufacture uses 900 kWh, repair 80; old operation uses 1.1 kWh and new 0.6 per service. What is the energy break-even count? 500 services because operation differs by 0.5. 1,960 services by adding manufacture and repair energy. 1,640 services by dividing the 820 initial-energy gap by 0.5 per service. Question 9 A scores 80 water, 50 material, 60 cost; B scores 60, 80, 70. Weights are 40%, 30%, 30%. Which is higher? B at 69 versus A at 65, subject to a separate eligibility gate. A at 190 versus B at 210 by simply adding raw scores. They tie because weights total 100%. Question 10 Ownership costs 12,000 plus 400 annual maintenance for three years with 2,000 residual; service costs 300 monthly. Which has lower undiscounted cash cost? Ownership 11,200 and service 10,800; ownership is lower. Ownership 11,200 and service 10,800; service is lower by 400. Ownership 13,200 and service 900 because residual value and term are ignored. Question 11 In 20-crate trials, A costs 50 each and delivers 600 cycles; B costs 65 each and delivers 900. What is purchase cost per cycle? A 0.083 and B 0.072 by dividing one unit price by all cycles. A 1.67 and B 1.44, so A is cheaper per cycle. A about 1.67 and B 1.44; B is lower on trial purchase cost per cycle. Question 12 Of 500 crates, 380 return within 14 days, including 30 unserviceable; another 50 return late. What is on-time serviceable return from the cohort? 350 ÷ 500 = 70%. 430 ÷ 500 = 86% because lateness is irrelevant. 380 ÷ 500 = 76% because every return is serviceable. Question 13 Of 120 devices entering repair, 90 restart, 72 remain working at day 90, and 12 have not finished follow-up. What is verified success among all entrants? 72 ÷ 120 = 60%, with the 12 pending. 90 ÷ 120 = 75% verified 90-day success. 72 ÷ 90 = 80% of all entrants, without showing the others. Question 14 Waste is 1,000 kg for 10,000 orders, then 750 kg for 8,000. What changes in total and per-thousand-order intensity? Both fall 40%, matching advertising. Both fall 25% because only waste mass changes. Total falls 25%; intensity falls from 100 to 93.75 kg, or 6.25%, if service is comparable. Question 15 Demand is 9,000 meals, 8,640 are served, and surplus is 150 kg against a 180-kg cap. Service must reach 98%. What is the judgement? Full success because surplus is below 180. Service is 96% and fails 98%; surplus passes its gate, so pause scaling unchanged. Service is 98% because surplus kilograms compensate unserved demand. Create a free account to mark your answers and save your progress.
