SOLUTION: Mary needs to row her boat across a 120 m -wide river that is flowing to the east at a speed of 1.3 m/s . Mary can row with a speed of 3.9 m/s .

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Question 1066665: Mary needs to row her boat across a 120 m -wide river that is flowing to the east at a speed of 1.3 m/s . Mary can row with a speed of 3.9 m/s .

Found 2 solutions by ikleyn, josgarithmetic:
Answer by ikleyn(52847) About Me  (Show Source):
You can put this solution on YOUR website!
.
1.  Uncompleted/broken post.

2.  The solution by "josgarithmetic" is WRONG.



Answer by josgarithmetic(39625) About Me  (Show Source):
You can put this solution on YOUR website!
tan%28theta%29=1.3%2F3.9=1%2F3
This angle theta, is 33.7 degrees, the angle from starting point, between the point directly accross the river and the point to the EAST accross the river. This ASSUMES Mary directs her boat at the given speed accross the current with its given speed.

r, actual speed in the found 33.7 degree direction
cos%2833.7%29=3.9%2Fr
r=3.9%2Fcos%2833.7%29
r=3.9%2F0.83195
highlight_green%28r=4.68%29, meters per second


Where on the other side of the river, but TO THE EAST, will Mary arrive?
Now, the right triangle is legs x and 120 meter, and theta 33.7 degree. The right angle is between the legs x and 120.
-
x%2F120=tan%2833.7%29
x=120%2Atan%2833.7%29
highlight_green%28x=80%29, meters to the east of the point directly accross the river from where she began.

--not completed--