The problem involves determining the salary of one friend (U) based on seating arrangement and salary constraints for six friends (P, Q, R, S, T, U).

Step-by-Step Deduction of Arrangement and Salaries

We will deduce the seating arrangement and salaries step-by-step using the given clues:

• There are 6 positions in a row. Let's denote them 1 to 6 from left to right.
• Clue: "P sits at the left end of the row and gets a salary of 1000."
  • Arrangement: $P _ _ _ _ _$
  • Salaries: $P(1000) _ _ _ _ _$
• Clue: "Q sits immediately before R and gets a salary of 800." This means QR is a block, and Q's salary is $800$.
• Clue: "Q is second to the left of S." This implies the pattern $_ Q _ S$.
• Combining "P at left end", "QR block", and "$_ Q _ S$":
  • If Q is at position 2, then S is at position 4. $P Q _ S _ _$.
  • Since QR is a block, R must be at position 3. $P Q R S _ _$.
  • This arrangement places Q (pos 2) second to the left of S (pos 4).
  Arrangement so far: $P(1000) Q(800) R(?) S(?) T(?) U(?)$ in positions 1 to 6.
• Clue: "T sits between U and S." This implies the sequence $U T S$ or $S T U$.
  • In our current arrangement $P Q R S _ _$, S is at position 4.
  • For T to be between S and U, the sequence must be $S T U$.
  • This means T is at position 5 and U is at position 6.
  Updated Arrangement: $P Q R S T U$
• Clue: "T gets a salary of 1500."
  • Salaries assigned: $P(1000) Q(800) R(?) S(?) T(1500) U(?)$
• Remaining salaries are $500, 1800, 2000$ for friends R, S, and U.
• Clue: "R gets a salary neither of 2000 nor of 1800."
  • Since R's salary cannot be $2000$ or $1800$, and the only other option is $500$, R must get $500$.
  Salaries: $P(1000) Q(800) R(500) S(?) T(1500) U(?)$
• Remaining salaries for S and U are $1800$ and $2000$.
• Clue: "The friend who gets a salary of 2000 does not sit at the extreme end of the row."
  • The extreme ends are position 1 (P) and position 6 (U).
  • U is at position 6 (an extreme end). Therefore, U cannot have the salary of $2000$.
  • This leaves $1800$ as the only possible salary for U.
  • Consequently, S must get the salary of $2000$.

Final Arrangement and Salaries

• Position 1: P (Salary $1000$)
• Position 2: Q (Salary $800$)
• Position 3: R (Salary $500$)
• Position 4: S (Salary $2000$)
• Position 5: T (Salary $1500$)
• Position 6: U (Salary $1800$)

Determining U's Salary

Based on the deduction, U sits at position 6 and gets a salary of $1800$.