Question 1204796
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Upstream, the rate is 6/2 = 3mph; downstream, it is 6/1.5 = 4mph.<br>
This "upstream, downstream" problem is a very common type of problem in which the sum of two numbers is A and the difference of those two numbers is B; in this problem those numbers are 4 and 3.<br>
If formal algebra is not required, this kind of problem is easily solved using logical reasoning.<br>
The boat speed, plus the current speed, is 4mph; the boat speed, minus the current speed, is 3mph.<br>
Picture those numbers on a number line.  When you start with the boat speed and add the current speed, the result is 4mph; when you start with the boat speed and subtract the current speed, the result is 3mph.<br>
Logic then tells you that the boat speed is halfway between 3mph and 4mph -- i.e., 3.5mph.  And then that means the current speed is 0.5mph.<br>
ANSWERS: Boat speed 3.5mph; current speed 0.5mph<br>
In general, for any problem like this...<br>
If A+B = m and A-B = n,
Then A is halfway between m and n (i.e., the average of m and n) and B is the difference between that average and either of m or n.<br>