testing header
Math Goodies is a free math help portal for students, teachers, and parents.
Free Math
Newsletter
 
 
Interactive Math Goodies Software

Buy Math Goodies Software
testing left nav
Math Forums @ Math Goodies
Math Forums @ Math Goodies
Home | Profile | Register | Active Topics | Members | Search | FAQ
 All Forums
 Homework Help Forums
 Basic Math and Pre-Algebra
 prime numbers

Note: You must be registered in order to post a reply.
To register, click here. Registration is FREE!

Screensize:
UserName:
Password:
Format Mode:
Format: BoldItalicizedUnderlineStrikethrough Align LeftCenteredAlign Right Horizontal Rule Insert HyperlinkInsert EmailInsert Image Insert CodeInsert QuoteInsert List Insert Special Characters Insert Smilie
   
Message:
* HTML is OFF
* Forum Code is ON

Math Symbols
Squared [squared] Cubed [cubed] Square Root [sqrt] Cube Root [cbrt] Pi [pi]
Alpha [alpha] Beta [beta] Gamma [gamma] Theta [theta] Angle [angle]
Degrees [degrees] Times [times] Divide [divide] Less Than or Equal To [less-than] Greater Than or Equal To [greater-than]
Plus Minus [plus-minus] Integral [integral] Sum [sum] Sub 1 [sub-1] Sub 2 [sub-2]
Element Of [element-of] Union [union] Intersect [intersect] Subset [subset] Empty Set [empty-set]

  Check here to subscribe to this topic.
 
   

T O P I C    R E V I E W
family187 Posted - 09/09/2009 : 17:46:05
my son has three problems for homework and it says remember the 1st prime numbers. I don't know what he means by that and the problems are 18, 25, and 30. Please help me with explaining the problems to him. HELP!!!!!
1   L A T E S T    R E P L I E S    (Newest First)
the_hill1962 Posted - 09/10/2009 : 07:40:25
Probably the problems are "prime factorization".
In these problems, you check to see which prime numbers go into the number to be factored. Therefore, a list of prime numbers (or memorizing the first ten or so):
2, 3, 5, 7, 11, 13, 17, 19, 23, 29...
These are prime numbers because the only numbers that divide evenly into them are 1 and itself.
For example, 6 is not a prime number because 6 divides by not only 1 and 6 but also 2 and 3.
7 is prime because only 1 and 7 go into it.
9 is not prime because 3 goes into it.
11 is prime because nothing except 1 and 11 go into it.
14 is not prime because 2 and 7 go into it.
Okay, for the first problem "18", check to see which prime number go into it. Check 2, 3. Note that there is no need to go further. You only need to check the primes that are less than the of the number. In this case, 18 = 4.2426.... and the prime number 5 is larger than that so does not need to be checked.
18 2 = 9. So "2" IS a prime factor.
18 3 = 6. So "3" IS a prime factor.
It gets a little more difficult than this. You need to see how many times those prime numbers go into 18.
To do this, just keep dividing successively:
182=9. 93=3. 33=1. So the prime factorization of 18 is 2132.
You see, you divided by 3 twice and 2 once.
Instead of doing 25 and 30 for you, here is another example:
Try 90:
You don't need to go past 90. That is, 9.48... So you list of possible primes is 2, 3, 5, 7.
902=45. 455=9. 93=3. 33=1.
So the prime factorization of 90 is 213251
Notice that the MathGoodies CD contains a lesson about this:
http://www.mathgoodies.com/lessons/toc_vol3.html
however it is not one of the free lessons.

Math Forums @ Math Goodies © 2000-2004 Snitz Communications Go To Top Of Page
This page was generated in 0.06 seconds. Snitz Forums 2000
testing footer
About Us | Contact Us | Advertise with Us | Facebook | Blog | Recommend This Page




Copyright © 1998-2014 Mrs. Glosser's Math Goodies. All Rights Reserved.

A Hotchalk/Glam Partner Site - Last Modified 21 May 2014