<PRE><B>Question 590248</B>
Richard used his kayak and rows upstream at the rate of 3 kph and rows back downstream at the rate of 21 kph. If the complete trip requires 30 minutes. Find the total distance Richard rowed. 
:
Let d = one-way distance rowed
then
2d = total distance
:
Change 30 min to .5 hrs
:
Write a time equation; time = dist/speed
{{{d/3}}} + {{{d/21}}} = .5
multiply by 21
21*{{{d/3}}} + 21*{{{d/21}}} = 21*.5
cancel the denominators
7d + d = 10.5
8d = 10.5
d = {{{10.5/8}}}
d = 1.3125 km one way
then
2 * 1.3125 = 2.625 km total distance
;
:
See if this checks out find the time each way
1.3125/3 = .4375 hrs
1.3125/21= .0625 hrs
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total time;.5 hrs; confirms our solution of 2.625 km total</PRE>