A boat goes 12 km downstream and comes back to the starting point in 3 hours if the speed of the cur...........

Quantitative Aptitude ( CCS) Boats and Streams

A boat goes 12 km downstream and comes back to the starting point in 3 hours . if the speed of the current is 3 km/hr, then the speed of the boat in still water is

12 km/h

9 km/h

8 km/h

6 km/h

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Explanation:

12/(x + y) + 12/(x - y) = 3
Speed of the current, y = 3 km/h
12/(x + 3) + 12/(x - 3) = 3
In such type of question take help from the options to
save your valuable time.
Take option (b) x = 9
12/(9 + 3) + 12/(9 - 3) = 12/12 + 12/6 = 1 + 2 = 3
Thus, Option (b) is the answer
Alternate:
T = 2xD/(x²– y²),
3 = 2 × x × 12/(x² - 32)
3 (x² - 9) = 24x
x² – 8x – 9 = 0
x = 9 – 1
x = 9 km/hr