dilr seating arrangement problem

Question

Seven bays are arranged in a circle and numbered 1 to 7 in the clockwise direction. Four drones — Wisp, Xenon, Yara and Zephyr — rest on four of the seven bays; the other three bays are empty. On each turn the drone whose turn it is moves either clockwise or anticlockwise (its own choice) and lands on the FIRST empty bay reached in the chosen direction. The turns occur in this order: Wisp (Turn 1), Xenon (Turn 2), Yara (Turn 3), Zephyr (Turn 4), Wisp (Turn 5), Xenon (Turn 6), Yara (Turn 7). "Four consecutive bays" means four bays whose numbers are consecutive around the circle (e.g., 6,7,1,2). In the STARTING position (before Turn 1): Xenon and Yara rest on two adjacent bays, while each of Wisp and Zephyr has an empty bay on both of its sides.
The following is known.
1. The four drones occupy four consecutive bays ONLY at the end of Turn 3 and at the end of Turn 5 (and at no other time, including the start).
2. Zephyr is on Bay 6 after Turn 1 and on Bay 5 after Turn 5; Yara is on Bay 3 after Turn 2
.
Which bay was initially occupied by Xenon (before Turn 1)?

A Bay 3
B Bay 4
C Bay 6
D Bay 1

Q2. Which drone occupied Bay 7 at the end of Turn 4?

A Wisp
B Xenon
C Yara
D Zephyr

Q3. Which set of bays was occupied at the end of Turn 5?

A Bays 1, 5, 6 and 7
B Bays 2, 5, 6 and 7
C Bays 1, 2, 6 and 7
D Bays 1, 2, 5 and 6

Q4. For how many of the four drones can the bay occupied at the end of Turn 7 be uniquely determined?

A 1
B 2
C 4
D 3

please explain me this question puzzle its so complicated

|| These questions force me to think whether I will be going to score good in the exams ||😫

nav · Accepted Answer

so it is given that there are 7 bays and 4 drones so first draw a rough circle with 7 points as positions. clue 2 says Zephyr is on Bay 6 after Turn 1 and since turn 1 is of W, so Z hasnt moved so his initial position has to be 6, same way it says Yara is on Bay 3 after Turn 2 and Y's turn doesnt come till turn 3 so Y's initial position has to be 3. the question also says Xenon and Yara rest on two adjacent bays, while each of Wisp and Zephyr has an empty bay on both of its sides, so X has to be at 4 and W on bay 1. this gives initial arrangement.

now for turn 1 if W goes from 1 -> 2, then in turn 2 X can go from 4 -> 1 and for turn 3 Y can go from 3 -> 7. this satisfies the clue 1 that he four drones occupy four consecutive bays at the end of Turn 3.

then for turn 4, Z moves from 6 -> 5, for turn 5 W moves from 2 -> 6. this again satisfies clue 1 the four drones occupy four consecutive bays ONLY at the end of Turn 3 as well as Turn 5 and also satisfies Zephyr is on Bay 5 after Turn 5.

now for turn 6, x can move from 1 -> 2 and for turn 7 Y can move either from 7 -> 1 or 7 to 7 -> 4.

this arrangement satisfies all constraints. to solve such questions, we have to execute such a hit and trial method to satisfy all positions.

Answers:
Q1.  B
Q2. C
Q3. A
Q4. D

dilr seating arrangement problem

1 Answer