SOLUTION: Ming's boat goes 20 mph in still water. It travels 75 miles upstream and back in a total time of 8 hours. what is the speed of the current?

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Question 1095472: Ming's boat goes 20 mph in still water. It travels 75 miles upstream and back in a total time of 8 hours. what is the speed of the current?
Found 2 solutions by ikleyn, Alan3354:
Answer by ikleyn(52879)   (Show Source): You can put this solution on YOUR website!
.
 +  = 8.


Solve for c, the speed of the current.


To solve it, multiply both sides by (20-c)*(20+c) = 400-c^2.


Then solve the obtained quadratic equation for c to get the 


Answer.  c = 5 miles per hour.


It is a typical and standard Upstream and Downstream round trip word problem.
You can find many similar fully solved problems on upstream and downstream round trips with detailed solutions in lessons
    - Wind and Current problems
    - More problems on upstream and downstream round trips
    - Wind and Current problems solvable by quadratic equations
    - Unpowered raft floating downstream along a river
    - Selected problems from the archive on the boat floating Upstream and Downstream
in this site.

Read them attentively and learn how to solve this type of problems once and for all.

Also,  you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this textbook under the section "Word problems",  the topic "Travel and Distance problems".


Save the link to this online textbook together with its description

Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson

to your archive and use it when it is needed.



Answer by Alan3354(69443)   (Show Source): You can put this solution on YOUR website!
Ming's boat goes 20 mph in still water. It travels 75 miles upstream and back in a total time of 8 hours. what is the speed of the current?
----------
c = current
75/(20-c) + 75/(20+c) = 8
75*(20-c) + 75*(c+20) = 8(400 - c^2) = 3200 - 8c^2
3000 = 3200 - 8c^2
8c^2 = 200
c^2 = 25
c = 5 mi/hr
==================================
If you mean it's 75 miles round-trip, do it the same way.
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