BOATS SET1

Q.1 A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) & stream ?
A) 3:1
B) 2:1
C) 4:1
D) 5:1
Ans. A
Let upstream =2x km/hr
Downstream = x km/hr
Boat:Stream = (u+v/2) : (u-v/2)
(2x+x / 2) : (2x-x / 2)

Q.2 Boat covers a certain distance downstream in 1 hr, while it comes back in 1 ½ hrs. If the speed of the stream be 3 km/hr. What is the speed of the boat in still water ?
A) 15 km/hr
B) 16 km/hr
C) 17 km/hr
D) 18 km/hr
Ans. A
Shortcut:
Speed= Z(x+y) / y-x
Or 3 (1+ 3/2) / (3/2 – 1)
= 15 km/hr

Q.3 A man can row 15km/hr in still water. If he takes twice as long to row up as to row down the river. Find the rate of the stream ?
A) 5 km/hr
B) 6 km/hr
C) 7 km/hr
D) 8 km/hr
Ans. A
Shortcut:
15+x = 2 (15 – x)
15+x = 30-2x
Thus, x=5km/hr

Q.4 Man can row 8km/hr in still water & the river is running at 2km/hr. If the man takes 1hr to row to a place & back. How far is the place ?
A) 3.75 km
B) 4.75 km
C) 3.0 km
D) 4.0 km
Ans. A

Q.5 Man can row upstream at 10 km/hr & downstream at 16 km/hr. Find the man’s rate in still water & the rate of current ?
A) 13 & 3 km/hr
B) 12 & 2 km/hr
C) 11 & 1 km/hr
D) 13 & 2 km/hr
Ans. A
Rate in still water = ½ (10+16) = 26/2 = 13 km/hr
Rate of current = ½ (10-16) = 3 km/hr