Correct Answer - Option 3 : 6
Given:
A boat goes 8 km upstream and 8 km downstream in 3 hours
The speed of the current is 2kmph
Formula Used:
Time = Distance/Speed
Speed of upstream = (x – y)
Speed of downstream = (x + y)
Where, x = Speed of boat in still water
y = Speed of current
Calculation:
According to the question
[8/(x - 2)] + [8/(x + 2)] = 3
⇒ 2x/(x2 – 4) = 3/8
⇒ 16x = 3x2 – 12
⇒ 3x2 - 16x - 12 = 0
⇒ 3x2 - 18x + 2x - 12 = 0
⇒ 3x(x - 6) + 2( x - 6) = 0
⇒ (3x + 2) (x - 6) = 0
⇒ x = -2/3 (not possible) or x = 6
∴ x = 6 kmph = speed of boat in still water.