A print shop in Bukhara received an urgent order on a Thursday morning: 3,000 brochures for a tourism fair that opened at noon. The shop has two printers. The old one would need 6 hours to print the whole order alone. The new one would need 3 hours.
The shift manager, Sanjar, had a deadline. The brochures had to be ready by 11 o'clock so that a van could deliver them before the fair opened. It was already 9.
A new employee said they would need four and a half hours, the average of 6 and 3. Sanjar laughed. "If the new printer can do it alone in 3 hours, adding a second printer cannot make it slower," he said.
He thought about each machine's rate instead. In one hour the old printer does one sixth of the job and the new one does one third. Working together, they do one sixth plus two sixths, which is half of the job in an hour. The whole order would take 2 hours.
He started both printers at 9 o'clock. At 11, the last stack of brochures came out warm, and the van left on time. On the way back, the driver asked why they had not simply used the new printer. "Then we would have finished at noon," Sanjar said, "and the fair would have opened without us."
Since that day, every urgent order in the shop starts with the same question: not how long each machine takes, but how much of the job each machine does in an hour.