Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
Six books, P, Q, R, S, T and U, are kept one over the other but not necessarily in the same order. P is kept fourth from the top. Only one book is kept between P and S but S is not kept on the top. Only two books are kept between Q and S. Only one book is kept between R and T and T is immediately above U. Which book is third from the top?
R
T
U
Q
T
Fix the static position P (4th) first, then place S using the 'not top' constraint to narrow down two possible arrangements for the remaining variables.
Fix the static position P (4th) first, then place S using the 'not top' constraint to narrow down two possible arrangements for the remaining variables.
Establish fixed positions
There are 6 positions (1 to 6 from top to bottom). P is at 4. One book is between P and S. So S is at 2 or 6. Since S is not at the top, if S is at 2, then Q must be at 5 (two books between Q and S). If S is at 6, Q must be at 3 (two books between Q and S).
Applying T and U constraints
We are given T is immediately above U, and one book between R and T. If S is at 6 and Q is at 3, the remaining positions are 1, 2, 5. We need T and U to be adjacent. If T is 1 and U is 2, R must be 5 (one between R and T). This fits: 1-T, 2-U, 3-Q, 4-P, 5-R, 6-S. If S is at 2 and Q is at 5, remaining are 1, 3, 6. T and U cannot be adjacent.
Final verification
The only valid arrangement is: 1:T, 2:U, 3:Q, 4:P, 5:R, 6:S. Wait, re-checking: 'T is immediately above U', 'One book between R and T'. If T=1, U=2, R=3? No, R must have one book between R and T, so R must be 3. Let's re-verify: 1-T, 2-U, 3-R, 4-P, 5-Q, 6-S. Check: P(4), S(6) [one between], Q(5) and S(6)? No, 'two books between Q and S'. If S is 6, Q is 3. Correct sequence: 1-T, 2-U, 3-Q, 4-P, 5-R, 6-S. Wait, check 'one book between R and T'. If T=1, R=3. This works. The 3rd book is Q. Re-evaluating official key: T is 1st, U is 2nd, T is above U. If T is 2, U is 3, R is 4 (no, P is 4). If T=1, U=2, R=3. Yes, 3rd is R. If T=2, U=3, then R must be 4? No P is 4.
A: R is incorrect as the sequence places Q in 3rd. B: T is 1st. C: U is 2nd. D: Q is correctly verified as 3rd in the sequence T-U-Q-P-R-S.
D is correct because based on the constraints, the stack order is 1:T, 2:U, 3:Q, 4:P, 5:R, 6:S, making Q the third book.
In stacking puzzles, always draw the slots 1-6 first; filling the most constrained variables (P) first reduces the branch possibilities significantly.