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Finding Speed, Distance, and Time

Date: 10/31/2002 at 09:07:29
From: Valerie Lynch
Subject: Science

Time = distance/speed. Does this symbol (/) mean that distance divided 
by speed will give you time?


Date: 10/31/2002 at 10:11:58
From: Doctor Ian
Subject: Re: Science

Hi Valerie,

In a manner of speaking, yes.  We _define_ speed as distance divided
by time, 

  speed = distance / time

but once we have the equation, we can use any of its variations, 

  speed    = distance / time

  distance = speed * time

  time     = distance / speed

to compute any one of the quantities when we happen to know the other
two. 

For example, suppose we drive for 2 hours at 30 miles per hour, for a
total of 60 miles. If we know the time and the speed, we can find the
distance:

  2 hours * 30 miles/hour = 60 miles

If we know the time and the distance, we can find the speed:

  60 miles / 2 hours = 30 miles/hour

If we know the speed and the distance, we can find the time:

  60 miles / (30 miles/hour) = 2 hours

It's a little like having a family of multiplication facts, e.g., 

  12 = 3 * 4

   3 = 12 / 4

   4 = 12 / 3

Does this make sense? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/ 
Associated Topics:
Middle School Equations

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