- Quantity A > Quantity B
- Quantity A < Quantity B
- Quantity A = Quantity B
- Quantity A ≤ Quantity B
- Quantity A ≥ Quantity B
Option 2 : Quantity A < Quantity B
Quantity A:
Ratio of speed of boat to speed of stream = 2 : 1
Let Speed of Boat, SB = 2a and Speed of Stream, SS = a
TU + TD = Total time taken
⇒ Distance/ (Speed of boat downstream) + Distance/ (Speed of boat upstream) = Total Time taken
⇒ 162/ (2a + a) + 162/ (2a - a) = 36
⇒ 162 × = 36
⇒ (2a - a + 2a + a)/((2a + a) × (2a - a)) = 36/162
⇒ 4a/3a² = 2/9
⇒ 36a = 2 × 3a²
⇒ a = 6 km/hr
SS = 6 km/hr and SB 12 km/hr
Difference in time = 162/(12 - 6) - 162/(12 + 6) = 27 - 9 = 18 hours
Quantity B:
Let Speed of boat, SB = a km/hr
T - (TD + TU) = 7.5
⇒ 60/(a - 6) - 30/(a - 6) - 30/(2a - 6) = 7.5
⇒ 30/(a - 6) - 30/(2a - 6) = 7.5
⇒ 30 = 7.5
⇒ (2a - 6 - a + 6)/((a - 6)(2a - 6)) = 7.5/30
⇒ a/((a - 6)(2a - 6)) = 1/4
⇒ (a - 6)(2a - 6) = 4a
⇒ 2a² - 6a - 12a + 36 = 4a
⇒ 2a² - 22a + 36 = 0
⇒ a² - 11a + 18 = 0
⇒ a² - 2a - 9a + 18 = 0
⇒ a(a - 2) - 9(a - 2) = 0
⇒ (a - 2)(a - 9) = 0
⇒ a = 9 km/hr and 2 km/hr
Speed of boat is always greater than the speed of stream so, SB = 9 km/hr
Total time taken = 60/(9 + 6) + 60/(9 - 6) = 4 + 20 = 24 hours
∴ Quantity A < Quantity B