Doubt: LRDI Scheduling & Sequencing — PixelMend walk-in repair counter - waved FCFS device servicing

21d ago

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for tablet service.........each wave will have exactly 3 devices and that are handled by 2 technicians , therefore here we have an overlap of waves for tablet services of 3 mins. hence wave at 9.15 which is wave 2 will actually start at 9.18...........so as given in question work on K's and L's tablet will start at 9.18 and end at 9.24 then which work on M's tablet will start at 9.24 and end at 9.30. whereas for laptops, there is only 1 technician and there are only 2 laptops per wave and total time taken for these each wave is 14 min hence time for each wave can be calculated independently , so for wave 2 , work on F's laptop will start at 9.15 and end at 9.22 and work on G's laptop will start at 9.22 and end at 9.29 hence here both the options B and C are false (not correct)

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PixelMend walk-in repair counter - waved FCFS device servicing · Q0

Scheduling & SequencingEasy

Set Setup · Scheduling & Sequencing

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PixelMend, a walk-in device-repair counter, attended to exactly 120 customers one Sunday. Customers were admitted in twelve waves of ten, one wave every 15 minutes starting at 9:00 AM (so the waves began at 9:00, 9:15, 9:30, ... up to 11:45 AM). Every customer in a wave is treated as arriving at that wave's start time. Each customer brought exactly one device needing exactly one kind of service - Phone, Laptop or Tablet - and PixelMend has dedicated technicians for each: three Phone technicians, one Laptop technician and two Tablet technicians. Within a service type, devices are taken up strictly first-come-first-served: the instant a technician of that type is free, the next waiting device of that type (in the order its owner was admitted) is taken up. A Phone service takes 5 minutes, a Laptop service 7 minutes and a Tablet service 6 minutes. The number of devices of each service type was the same in every wave. 1. Exactly half of all the devices brought to PixelMend that day were Phones. 2. For each of the three service types, the number of devices of that type was the same in every wave. 3. In the 9:15 AM wave, Farida and Gagan had both brought Laptops, and they were taken up in that order. 4. In the 9:15 AM wave, Kavya, Lalit and Meera had all brought Tablets, and they were taken up in that order. 5. Every wave was completely full (each wave had exactly ten customers), and no customer brought more than one device.

Considering only Farida, Gagan, Kavya, Lalit and Meera, which of the following statements is FALSE?

1 Answer

CATLab AI✦ CATLab AI21d ago

This question turns entirely on when the 9:15 wave's tablets can start — and the "3-minute spillover" from wave 1 doesn't actually happen, because the two tablet technicians work side by side, not one after another.

First, pin down the mix per wave. Exactly half of 120 customers brought phones, so $60 \div 12 = 5$ phones per wave. Each wave has 10 customers, leaving 5 others, and the 9:15 wave shows us the split: 2 Laptops (Farida, Gagan) + 3 Tablets (Kavya, Lalit, Meera). Since each type's count is constant across waves, every wave has 5 phones, 2 laptops, 3 tablets.

Now check whether wave 1's tablets delay wave 2. Wave 1's three tablets arrive at 9:00:

Technician 1: tablet 1, 9:00–9:06
Technician 2: tablet 2, 9:00–9:06
Whichever technician frees first takes tablet 3: 9:06–9:12

Both technicians are free by 9:12 — three minutes before the 9:15 wave. The 3-minute overlap in your working comes from $3 \times 6 = 18$ minutes, but that adds up the two technicians' work as if done serially. In parallel, a wave's tablet load clears in $6 + 6 = 12$ minutes, which fits inside the 15-minute gap. So wave 2's tablets start right at 9:15, not 9:18.

Wave 2 tablets (2 technicians, 6 min each): Kavya and Lalit start together, 9:15–9:21. Meera must wait for a free technician, so 9:21–9:27.

Wave 2 laptops: your working here is exactly right — with one technician, $2 \times 7 = 14$ minutes < 15, so no carry-over (wave 1's laptops even finish by 9:14). Farida 9:15–9:22, Gagan 9:22–9:29.

Ready times:

Customer	Device	Ready at
Kavya	Tablet	9:21
Lalit	Tablet	9:21
Farida	Laptop	9:22
Meera	Tablet	9:27
Gagan	Laptop	9:29

Testing each option:

(A) Kavya 9:21 before Gagan 9:29 — true. (B) Gagan 9:29 is the last of the five — true. (C) Meera 9:27 before Farida 9:22 — false; Meera actually finishes after Farida. (D) Lalit 9:21 before Meera 9:27 — true.

(Useful sanity check: under the 9:18 start, both B and C came out false for you. When a "find the false statement" question yields two false options, the assumed timeline is usually the culprit.)

Final answer: C

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Doubt: LRDI Scheduling & Sequencing — PixelMend walk-in repair counter - waved FCFS device servicing

janvia00

21d ago

🧩 LRDI Doubts

Customer

Device

Ready at

Kavya

Tablet