<PRE><B>Question 357289</B>
1) Normally I drive to work at 60km/h. 
If I drive at 72km/h I cut 8 minutes off my time for the trip.
 What distance do I travel?
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Let d = his travel distance
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Change min to {{{8/60}}} hrs
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Write a time equation; time = dist/speed
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60km time - 8 min = 72km time
{{{d/60}}} - {{{8/60}}} = {{{d/72}}}
Multiply by 720 to get rid of the denominators, results:
12d - 12(8) = 10d
12d - 96 = 10d
12d - 10d = 96
2d = 96
d - {{{96/2}}}
d = 48 km distance traveled
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Check this by finding the actual times
48/60 = .8 hrs
48/72 = .67 hrs
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differ: .13 hrs which is 8 min
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2) My motor boat normally travels at 24km/h in still water.
 One day I traveled 36 km against a constant current in a river.
 if i had travelled with the current, I would have traveled 48km in the same time.
 How fast was the current?
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Let c = the rate of the current
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Write a time equation, Time = dist/speed
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Against time = with time
{{{36/((24-c))}}} = {{{48/((24+c))}}} 
Cross multiply
36(24+c) = 48(24-c)
864 + 36c = 1152 - 48c
36c + 48c = 1152 - 864
84c = 288
c = {{{288/84}}}
c = 3.43 km/h is the current
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Confirm this, find the times
{{{36/((24-3.43))}}} = 1.75 hrs
{{{48/((24+3.43))}}} = 1.75 hrs</PRE>