Math Goodies is a free math help portal for students, teachers, and parents.
|
Interactive Math Goodies Software

testing left nav
Math Forums @ Math Goodies
Home | Profile | Register | Active Topics | Members | Search | FAQ
 All Forums  Homework Help Forums  Basic Math and Pre-Algebra  prime numbers New Topic  Reply to Topic  Printer Friendly
Author  Topic

family187
New Member

USA
1 Posts

 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!!!!!

the_hill1962

USA
1461 Posts

 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 213251Notice that the MathGoodies CD contains a lesson about this:http://www.mathgoodies.com/lessons/toc_vol3.htmlhowever it is not one of the free lessons.
Topic
 New Topic  Reply to Topic  Printer Friendly Jump To: Select Forum New Visitor Forum       Testing Forum Homework Help Forums       Basic Math and Pre-Algebra       Algebra       Geometry and Trigonometry       Pre-Calculus and Calculus       Probability and Statistics       Standardized Test Preparation Help       Miscellaneous Math Topics Educator Forum       Teacher Talk Parent Forum       Parent's Place  -------------------- Home Active Topics Frequently Asked Questions Member Information Search Page
 Math Forums @ Math Goodies © 2000-2004 Snitz Communications