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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

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