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The total time taken by a boat to travel \(x\) km downstream and \((x - 5)\) km upstream was 569.2 minutes. If the difference between the speed of the boat downstream and that in upstream is 3 kmph and the respective ratio between speed of boat in still water and speed of water current was (9 : 1), what is the value of x?
A) 63.8
B) 34.4
C) 29.4
D) 68.8
E) 62.5
Let the speed of the boat in still water be B km/hr
Let the speed of water current be S km/hr.
Downstream speed = B + S
Upstream speed = B - S
Given data 1: Difference between speed of boat downstream and that upstream = 3 km/hr
So, (B + S) - (B - S) = 3
Or 2S = 3 or S = 1.5 km/hr.
Given data 2: Ratio between speed of boat in still water and speed of water current was (9 : 1)
B : S = 9 : 1
If S = 1.5 km/hr, B = 9*1.5 = 13.5 km/hr
The boat travels x km downstream. i.e., the boat travels x km @ (13.5 + 1.5) = 15 km/hr
The boat travel (x - 5) km upstream. i.e., the boat travels (x - 5)km @ (13.5 - 1.5) = 12 km/hr
Given data 3: Total time taken = 569.2 minutes = \(\frac{569.2}{60}\) hours.
Total time taken = \(\frac{x}{15} + \frac{{x - 5}}{12} = \frac{569.2}{60}\)
\(\frac{{4x + 5x - 75}}{60} = \frac{569.2}{60}\)
\(\frac{{9x - 75}}{60} = \frac{569.2}{60}\)
or 9x - 75 = 569.2
So, 9x = 644.2
x = 71.57
None of the answer choices match. Could you please check the answer options?
You are wrong in highlighted portion..