A boat goes 140 km upstream in 28 hours and a distance of 203 km downstream in 29 hours. Find the speed of the boat in still water. (In kmph)

एक नाव धारा की विपरीत दिशा में 140 किमी की दूरी 28 घंटे में तय करती है और धारा की दिशा में 203 किमी की दूरी 29 घंटे में तय करती है। स्थिर जल में नाव की चाल ज्ञात कीजिए। (किमी प्रति घंटे में)

a) 6
b) 3
c) 1
d) 5

Answer : a) 6

Uttar Pradesh Police Sub-Inspector Exam

Solution :

Let the speed of the boat in still water is B km/h
Let the speed of the stream is S km/h

Upstream speed = B – S
Downstream + B+S

Distance = speed x time

In Upstream :
140 = (B – S) x 28
B – S = 5

In Downstream :
203 = (B+S) x 29
B + S = 7 -> S= 7-B

Put this value in B-S=5
B – (7-B) =5 => B +B -7 =5
=>2B = 12
=> B = 6 km/h

speed of the boat in still water is 6 km/h