SOLUTION: The current in a stream moves at a speed of 8 km/h. A boat travels 15 km upstream and 15 km downstream in a total time of 2 hr. What is the speed of the boat in still​ water

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Question 1057406: The current in a stream moves at a speed of 8 km/h. A boat travels 15 km upstream and 15 km downstream in a total time of 2 hr. What is the speed of the boat in still​ water?
Found 2 solutions by jorel555, ikleyn:
Answer by jorel555(1290) About Me  (Show Source):
You can put this solution on YOUR website!
Let s be the speed of the boat in still water. Then:
15/(s+8) + 15/(s-8)=2
15(s-8)+15(s+8)=2(sē-64)
2sē-30s-128=0
sē-15s-64=0
Using the quadratic formula, s+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+, we get two roots of 18.4658560997 and -3.46585609973. Throwing out the negative result, we get the speed of the boat in still water to be 18.47 kph. ☺☺☺☺

Answer by ikleyn(52775) About Me  (Show Source):
You can put this solution on YOUR website!
.
For detailed solutions of Upstream-Downstream Travel and Distance problems see the lessons
    - Wind and Current problems
    - More problems on upstream and downstream round trips
    - Selected problems from the archive on the boat floating Upstream and Downstream

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".