Question

A motor boat goes down stream 30km and again returns to the starting point
in a total time of 4 hours and 30 minutes. If the speed of the stream is 15km/hr,
then find the speed of the motor boat in still water.​

Answer 1

Step-by-step explanation:

Let the speed of the stream be x km/hr

Speed downstream =(15+x)km/hr

Speed upstream =(15−x)km/hr

Distance travelled downstream=30km

Distance travelled upstream=30km

Time upstream=

Speed upstream

Distance upstream

Time upstream=

15−x

30

Time downstream=

Speed downstream

Distance downstream

Time downstream=

15−x

30

Total time taken 4.5hrs

4.5=

15−x

30

+

15+x

30

4.5=

225−x

2

30(15+x)+30(15−x)

4.5=

225−x

2

900

225−x

2

=200

x

2

=25

x=5km/hr