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Date: Fri, 17 Mar 1995 14:35:24 AST
From: Richard Seguin

I have a question like this that I do not know how to do. 

Nancy ran a distance of 3.8km in 55 min. Calculate her speed. 

A) Kilometers per hour.
B) Metres per second.

Date: 5 Apr 1995 15:50:53 -0400
From: Dr. Ken
Subject: Re: conversion factors

Hello there!

I actually didn't learn a good solid way to do these questions until I was
in high school, because everyone assumed I already knew how to do them.
Here's how I'd approach it.

If she ran 3.8 km in 55 minutes, then her speed in km/min. is

3.8 km
------  = .069 km/min.
55 min.

To change units, we want to take this figure and multiply it by 1 a whole
bunch of times, which won't change the speed.  For example, to change the
minutes to hours, we know that 1 hour = 60 minutes, so we have

3.8 km     60 min.
------  x  -------
55 min.    1 hour

Notice that the minutes in the top and the bottom cancel out.  So we're left

3.8 x 60 km
-----------   =  4.1 km/hr.
55 x 1 hours

Now see if you can do the second one, noting that 1 km = 1000 m, and 
1 minute = 60 seconds.  Good luck!

-Ken "Dr." Math

Date: Fri, 17 Mar 1995 18:39:18 AST
From: Richard Seguin

For this Question:

In 1956 Australia won the women's 400-m freestyle relay. the race was won 
in 4 min 17.1s. Calculate the speed in metres per second. 

My formula would be: V=D   400m
                       -   ---- =1.6m/s if I were to round it off.
                       T   257.1s

Is this right?

Date: 5 Apr 1995 22:12:41 -0400
From: Dr. Ken
Subject: Re: conversion factors

Yes, that's exactly right!  Remember, units of measurement cancel just 
like everything else does, so when you're done, you can make sure 
eveything canceled except what you wanted there.  Keep it up!

-Ken "Dr." Math
Associated Topics:
Middle School Word Problems

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