ITPEC IP October 2022 Question 57
The PC on one’s desk and the printer in a shared space are started by a single person under the conditions shown in the figure below. It is only possible for the operations and processing of the PC and printer and the movement of the person to be performed sequentially, but during automatic processing of one device, it is possible for the person to move or operate the other device, or for the other device to perform automatic processing. What is the required time (in seconds) for the person to start the PC startup at his/her desk, then move and start and end the printer startup, return to his/her desk, and end the PC startup?
Flow of PC startup
Flow of printer startup
Explanation
223 seconds — the printer trip fits inside the PC's 150-second login-screen startup, so the PC's own steps set the total.
Timeline in seconds from the start:
- •0–3: A, turn on the PC (manual); B, the login-screen startup, then runs by itself until 153
- •3–63: walk to the printer
- •63–66: E, turn on the printer (manual); F, the printer startup, then runs by itself until 126
- •66–126: walk back to the desk while F runs
- •126–153: wait for B to finish
- •153–163: C, login operation (manual)
- •163–223: D, application startup, ends at 223
The PC's chain alone takes 3 + 150 + 10 + 60 = 223 seconds, and the person's trip, 60 + 3 + 60 = 123 seconds after turning the PC on, is over before B ends, so it adds nothing.
Answer (a)
Why not others:
- •(b) 256 — waits at the printer until F ends at 126 before walking back, arriving at 186; C and D then end at 186 + 10 + 60 = 256. The person may move while a device processes automatically
- •(c) 286 — 3 + 150 + 10 + 60 + 3 + 60: every operation and processing time in series, with only the walking left out; the automatic processing is meant to overlap other work
- •(d) 406 — 286 + 60 + 60: everything in series, both walks included, with no overlap at all
Key rule: Draw one timeline per resource: manual steps occupy the person, automatic steps occupy only the device, and the total is set by the longest chain of steps that must follow one another.
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