Question 1
There are 10 seats in a row, all facing North. 8 persons D, F, C, A, H, E, G and B are seated, leaving 2 seats empty.
D sits at seat 3. B sits at seat 8.
One empty seat is at an extreme end. F sits immediately to the right of an empty seat.
A sits fourth to the left of B.
How many persons sit between the two empty seats?
Solution Approach:
Step 1: Mark total positions
Seats: 1 2 3 4 5 6 7 8 9 10
Total: 10 seats, 8 persons, 2 empty.
Step 2: Place definite positions
- D at seat 3
- B at seat 8 (seat 8)
- One empty seat at extreme end β seat 1 is empty
Seat: 1(_) 2(_) 3(D) 4(_) 5(_) 6(_) 7(_) 8(B) 9(_) 10(_)
Step 3: Apply empty seat adjacency
- F sits immediately to the RIGHT of an empty seat
- Empty at seat 1 β seat 2 = F β
Seat: 1(_) 2(F) 3(D) 4(_) 5(_) 6(_) 7(_) 8(B) 9(_) 10(_)
Step 4: Apply "fourth to the left" condition
- A sits fourth to the LEFT of B (seat 8)
- Fourth to left: 8 β 7 β 6 β 5 β 4
- A at seat 4 β
Seat: 1(_) 2(F) 3(D) 4(A) 5(_) 6(_) 7(_) 8(B) 9(_) 10(_)
Step 5: Locate second empty seat
Remaining persons: H, E, G, C β fill seats 5, 6, 7, 9, 10 minus one empty.
After placing H(5), E(6), G(7), C(10): seat 9 is empty.
Step 6: Final arrangement
Seat: 1(_) 2(F) 3(D) 4(A) 5(H) 6(E) 7(G) 8(B) 9(_) 10(C)
Count persons between empty seats (seat 1 and seat 9):
Seats 2 through 8: F, D, A, H, E, G, B = 7 persons
Verification:
β D at seat 3
β B at seat 8
β Empty at seat 1 (extreme end)
β F immediately right of empty seat 1
β A fourth to left of B (seat 4 = seat 8 - 4)
Answer: 7 persons sit between the two empty seats.
Step 1: Mark total positions
Seats: 1 2 3 4 5 6 7 8 9 10
Total: 10 seats, 8 persons, 2 empty.
Step 2: Place definite positions
- D at seat 3
- B at seat 8 (seat 8)
- One empty seat at extreme end β seat 1 is empty
Seat: 1(_) 2(_) 3(D) 4(_) 5(_) 6(_) 7(_) 8(B) 9(_) 10(_)
Step 3: Apply empty seat adjacency
- F sits immediately to the RIGHT of an empty seat
- Empty at seat 1 β seat 2 = F β
Seat: 1(_) 2(F) 3(D) 4(_) 5(_) 6(_) 7(_) 8(B) 9(_) 10(_)
Step 4: Apply "fourth to the left" condition
- A sits fourth to the LEFT of B (seat 8)
- Fourth to left: 8 β 7 β 6 β 5 β 4
- A at seat 4 β
Seat: 1(_) 2(F) 3(D) 4(A) 5(_) 6(_) 7(_) 8(B) 9(_) 10(_)
Step 5: Locate second empty seat
Remaining persons: H, E, G, C β fill seats 5, 6, 7, 9, 10 minus one empty.
After placing H(5), E(6), G(7), C(10): seat 9 is empty.
Step 6: Final arrangement
Seat: 1(_) 2(F) 3(D) 4(A) 5(H) 6(E) 7(G) 8(B) 9(_) 10(C)
Count persons between empty seats (seat 1 and seat 9):
Seats 2 through 8: F, D, A, H, E, G, B = 7 persons
Verification:
β D at seat 3
β B at seat 8
β Empty at seat 1 (extreme end)
β F immediately right of empty seat 1
β A fourth to left of B (seat 4 = seat 8 - 4)
Answer: 7 persons sit between the two empty seats.