Question

A boat starting from point P goes downstream to point Q in 3 hours and returns back from point Q to the point P in 4 hours. If the speed of the water is 3 km/h, find the speed of the boat in still water.

• A. 20 km/h
• B. 12 km/h
• C. 32km/h
• D. 21 km/h

Answer 1

Answer:

D. 21 km/h

speed in still water = V

speed of water =3

speed in downstream =V+3

speed in upstream =V-3

time taken downstream = 3hrs

time taken upstream = 4hrs

$d=(v+3)\times3$

$d=(v-3)\times4$

$(v+3)\times 3=(v-3)\times 4)$

$3v+9=4v-12$

$v=21$