SOLUTION: Rita rows 12 km upstream and 12 km downstream in 3 hours. The speed of her boat in still water is 9 km/hr. Find the speed of the stream. word problem for quadratic equations

Question 170853This question is from textbook
: Rita rows 12 km upstream and 12 km downstream in 3 hours. The speed of her boat in still water is 9 km/hr. Find the speed of the stream.
word problem for quadratic equations This question is from textbook

Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Let s=speed of stream

Remember, the distance-rate-time formula is

Divide both sides by r to solve for t.

Rearrange the equation.

So when she goes upstream (against the current), the stream is slowing her down. So this means that and . So the equation for the upstream portion of the journey is:

When she goes downstream (with the current), the stream is speeding her up. So this means that and . So the equation for the downstream portion of the journey is:

Now simply add these two equations together to get the total time 3 hours like this:

Multiply both sides by the LCD to clear the fractions.

FOIL

Distribute

Combine like terms.

Subtract 243 from both sides.

Divide both sides by .

Take the square root of both sides. Note: only the positive square root is considered.

So the speed of the stream is 3 km/hr

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