The 5-digit number PQRST (all distinct digits) is such that T is not 0. P is thrice T. S is greater than Q by 4, while Q is greater than R by 3. How many such 5-digit numbers are possible?
- A 3
- B 4
- C 5
- D 6
Show answer and explanation
Correct answer: B - 4
Conditions: P = 3T with T not 0, S = Q + 4 and Q = R + 3 (so S = R + 7), and all five digits distinct. P = 3T allows only T = 1 (P = 3), T = 2 (P = 6) or T = 3 (P = 9). S = R + 7 with S a digit allows only R = 0, 1 or 2, giving (R, Q, S) = (0, 3, 7), (1, 4, 8) or (2, 5, 9). Now combine and reject clashes. T = 1, P = 3: (0, 3, 7) clashes with P = 3; (1, 4, 8) clashes with T = 1; (2, 5, 9) works, giving 35291. T = 2, P = 6: (0, 3, 7) works, giving 63072; (1, 4, 8) works, giving 64182; (2, 5, 9) clashes with T = 2. T = 3, P = 9: (0, 3, 7) clashes with T = 3; (1, 4, 8) works, giving 94183; (2, 5, 9) clashes with P = 9. Valid numbers: 35291, 63072, 64182, 94183, a total of 4. The official UPSC key confirms option (b).