SOLUTION: Vinnie drives his car 156 miles and has average of a certain speed. If the average speed had been 5mph more. He could have traveled 168 miles jn the same length of time. What was h

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Question 1168709: Vinnie drives his car 156 miles and has average of a certain speed. If the average speed had been 5mph more. He could have traveled 168 miles jn the same length of time. What was his average speed?
Found 3 solutions by Boreal, MathTherapy, greenestamps:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
ave speed=x
x=156/t, where t is time in hours.
(x+5)=168/t, same t
so tx=156 and t=156/x
and t=168/(x+5)
set those equal
168x=156x+780
12x=780
x=65 mph original speed and takes 2.4 hours
drive 70 mph and go 168 miles in that same time interval.
the answer is 65 mph.
Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!

Vinnie drives his car 156 miles and has average of a certain speed. If the average speed had been 5mph more. He could have traveled 168 miles jn the same length of time. What was his average speed?
Let speed be S

Then we get the following TIME equation: 

168S = 156(S + 5) ------ Cross-multiplying

168S = 156S + 5(156)

168S - 156S = 5(156)

12S = 5(156)

Speed, or  

Answer by greenestamps(13200)   (Show Source): You can put this solution on YOUR website!
 


The times are the same, so the ratio of distances is equal to the ratio of speeds:





You can certainly solve this using formal algebra.  But you can also solve it (I think a bit more quickly) solving it using equivalent fractions.





In that simplified fraction the difference between the numerator and denominator is 1.  The problem tells us we want an equivalent fraction in which that difference is 5.  So get an equivalent fraction by multiplying numerator and denominator by 5:





ANSWER: his average speed is 65mph (it would be 70mph if he had been driving 5mph faster).


 

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