CBSE 10th Class Mathematics
Past year question paper
Year 2020
SET 1, Code Number – 30/5/1
Question Number – 37 [b]
speed, distance and time problem
use the relation of speed, distance and time
Deepak BoraNewbie
A motor boat whose speed is 18km/h in still water takes 1 hour more to go 24km upstream than to return downstream to the same spot. Find the speed of the stream.
Share
Speed of boat = 18 km/h
Let speed of the stream be =x km/h
Speed of upstream = ( 18 – x ) km/hr
Speed of downstream = ( 18 + x ) km/hr
Distance = 24 km
Time = Distance / Speed
As per question,
[24 / (18 – x)] – [24 / (18 + x)] = 1
24 { [1 / (18 – x)] – [1 / (18 + x) ] } = 1
[2x/(324 – x²)] = 1 / 24
324 – x² = 48
x² + 48x -324 = 0
[x +54] [x – 6] = 0
x = -54, x = 6
x = 6 km / hr
∴ Speed of stream =6 km / hr