college algebra word problem?

Question

A Mississippi riverboat can travel 70 kilometers downstream in 5 hours and can make the return trip in 7 hours. Find the speed of the boat in still water.

Answer 1

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Let speed of boat in still waters be x km / hour and speed of current be y km/ hour

DOWNSTREAM

-------------------------

SPEED = DISTANCE / TIME

( x+ y ) = 70/5 = 14 .............(A)

UPSTREAM

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SPEED = DISTANCE / TIME

x - y = 70/7 = 10 ..............(B)

(A) + (B)

2x = 24

x = 12km/ hour ANSWER

y = 2 km/ hour

CHECK

DOWNSTREAM = 70 / (12+2) = 5 hours

UPSTREAM = 70 / (12-2) = 7 hours

Answer 2

let

x = speed of the boat

y = speed of the river

5(x + y) = 70

x + y = 14

7(x - y) = 70

x - y = 10

x + y = 14

x - y = 10

2x = 24

x = 12 kph