A boat can travel 12.6 km downstream in 35 minutes. If the speed of the water current is \( \Large \frac{1}{4} \)th the speed of the boat in still water, what distance (in km) can the boat travel upstream in 28 minutes ?


A) 7

B) 7.5

C) 8.5

D) 6

Correct Answer:
D) 6

Description for Correct answer:
Rate downstream of boat

= \( \Large \frac{Distance}{Time} = (\frac{12.6}{\frac{35}{60}} ) \ kmph \)

= \( \Large \frac{12.6 \times 60}{35} = 21.6 \ kmph \)

Speed of current = x kmph (let)

\( \Large \therefore \) Speed of boat in still water = 4x kmph

\( \Large \therefore \) 4x + x = 21.6

=> 5x = 21.6

=> \( \Large x = \frac{21.6}{5} = 4.32 \ kmph \)

\( \Large \therefore \) Rate upstream of boat = 3x

= \( \Large 3 \times 4.32 = 12.96 \ kmph \)

\( \Large \therefore \) Required distance

= \( \Large (\frac{12.96 \times 28}{60}) \ km \)

= 6 km

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