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dbillings · Nov 18, 2009, 04:13 PM

Dan boated downstream with the current for 3 miles, then truned around and cam back to his starting point. If the total time was 4 hours and the current was 0.4 mile per hour, what is the speed dan can boat in still water?

Unknown008 · Nov 19, 2009, 08:03 AM

Ok, first, let the speed of the boat in still water be x m/s.

The speed of the boat downstream is (x + 0.4) m/s
The speed of the boat upstream is (x - 0.4) m/s

Now, using the distance, speed time formula;

$Time = \frac{Distance}{Speed}$

We get Time downstream = 3/(x+0.4) Let this be Td
Time upstream = 3/(x - 0.4) Ket this be Tu

Total time = 4 hours. Let this be Tt

So, $T_t = T_d + T_u$

Hence;

$4 = \frac{3}{(x+0.4)} + \frac{3}{(x - 0.4)}$

Can you solve it?