A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

A.
4
B.
5
C.
6
D.
1

• Explanation:
  
  Let the speed of the stream be x km/hr. Then,
  Speed downstream = (15 + x) km/hr,
  Speed upstream = (15 - x) km/hr.
  30/(15 + x) + 30/(15 - x) = 4 1/2
  900/(225 - x^2 ) = 9/2
  9x^2 = 225
  x2 = 25
  x = 5 km/hr.
• 12 years agoHelpfull: Yes(10) No(3)
• Let the speed of the stream be x km/hr. Then,
  
  Speed downstream = (15 + x) km/hr,
  
  Speed upstream = (15 - x) km/hr.
  
  30 + 30 = 4 1
  (15 + x) (15 - x) 2
  900 = 9
  225 - x2 2
  9x2 = 225
  
  x2 = 25
  
  x = 5 km/hr.
• 11 years agoHelpfull: Yes(1) No(1)