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anonymous
 one year ago
A boat travels at a rate of 15km/hr in still water . It travels 60km upstream in the same time that it travels 90km downstream. What is the rate of the current ?
anonymous
 one year ago
A boat travels at a rate of 15km/hr in still water . It travels 60km upstream in the same time that it travels 90km downstream. What is the rate of the current ?

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mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Current speed = c Boat speed is still water = s Boat speed upstream = s  c Boat speed downstream = s + c

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0speed = distance/time

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0distance = speed * time

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0You understand the table so far? dw:1435634606883:dw

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Mk but we don't know the time

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0dw:1435634823006:dw

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Using: distance = speed * time you get this system of equations: 60 = (15  c)t 90 = (15 + c)t

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0We solve both equation for t and set them equal to each other: \(t = \dfrac{60}{15  c} \) \(t = \dfrac{90}{15 + c} \)

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0\(\dfrac{60}{15  c} = \dfrac{90}{15 + c} \)

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0Cross multiply: 90(15  c) = 60(15 + c) Divide both sides by 10: 9(15  c) = 6(15 + c) 135  9c = 90 + 6c 15c = 45 c = 3

mathstudent55
 one year ago
Best ResponseYou've already chosen the best response.0The current is 3 km/h

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Okay I understand it I have 3 more problems like this but can u tell me if I am doing it right ?
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