Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

Scientific Notation


Date: 09/16/97 at 00:42:42
From: Aubin
Subject: Scientific notation

How do you do this problem? I don't understand how you're supposed to 
get the answer: 

   5x10 to the 3rd power = 5,000
   5x10 to the -3rd power = -5,000

Is this correct?


Date: 11/03/97 at 09:56:46
From: Doctor Pipe
Subject: Re: Scientific notation

Aubin,

The first part of what you wrote is correct; 5x10 to the 3rd power = 
5,000. The second part is not correct.

Writing a negative exponent, such as 10^-3 (read that as ten to the 
minus third power) is the same as writing 1/(10^3) (read that as one 
over ten to the third power). Notice that the exponent is negative 
when writing 10^-3 and positive when writing 1/(10^3) - yet the two 
numbers are equal.

Remember that any number to the zeroeth power, say 10^0, is equal 
to 1.  10^0 = 1; 5^0 = 1; 275^0 = 1.

Remember also that when multiplying two numbers written as 
base^exponent, if the base in both numbers is equal then we add 
together the exponents: 10^5 x 10^6
                        = 10^(5+6)
                        = 10^11.

If we have a number 10^5, what number do we multiply it by to get 1?
Well, 10^5 x 10^(-5)
      = 10^(5 + (-5))
      = 10^0
      = 1.

So if 10^5 x 10^(-5) = 1
then         10^(-5) = 1 / 10^5

So, since 10^3 = 1,000 then 10^(-3) = 1/(10^3) = 1/1,000 = 0.001 .
It follows from this that:

     5x10 to the -3rd power = 5 x 10^(-3) = 5 x 0.001 = 0.005 .

The reason for this can be seen by examining what numbers to the right 
of the decimal point represent. You know what numbers to the left of 
the decimal point represent: the units digit represents the numeral 
times 10^0 (any number to the 0th power is 1), the tens digit 
represents the numeral times 10^1, the hundreds digit represents the 
numeral times 10^2, and so on.

Well, to the right of the decimal point, the tenths digit represents 
the numeral times 10^-1, the hundredths digit represents the numeral 
times 10^-2, the thousandths digit represents the numeral times 10^-3, 
and so on.

It's important to understand exponents because exponents allow us to 
extend the range of numbers that we can work with by allowing us to 
easily write and work with very large and very small numbers.  It's so 
much easier to write:

     10^23

then to write:

     100,000,000,000,000,000,000,000

Or to write:

     10^(-23)

instead of:

     0.00000000000000000000001

Good luck and enjoy!

-Doctor Pipe,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/   
    
Associated Topics:
Elementary Large Numbers
Elementary Number Sense/About Numbers
Elementary Square Roots
Middle School Exponents
Middle School Number Sense/About Numbers

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/