Teacher2Teacher 
Q&A #4147 
View entire discussion [<< prev] [ next >>]
From: Jeanne To: Teacher2Teacher Public Discussion Date: 2000062815:50:23 Subject: Re: HELP... Greatest Common Factors This may sound silly, but one of the first things I do is make sure my students have read the entire problem. Some students don't realize that math problems require reading EVERY word. These students skim through and thus miss some important information. Ask your daughter to read it out loud for you slowly. This way you know she's read it, and she can get reacquainted with the problem herself. Here's another silly statement. I ask "What is 'ugly' about the problem?" In other words, what is/are stopping the student from proceeding. Sometimes it's a not knowing what some of the words mean. Sometimes it's not understanding the process. Sometimes it's not understanding the question. It could be a combination of any of these. For this particular problem, it critical your daughter know what a "GCF" is and what is meant by "divisible." Let's start with the fact that 850 is a "plain ol' common factor" of those two numbers. (We'll address the issue of 850 being the "greatest common factor" in just a bit.) If 850 is a factor of a number, n then n = 850 times a counting number, c or n = 850c, for short. Thus, the two numbers in your daughter's problem are from the following list of numbers: 850(1), 850(2), 850(3), 850(4), 850(5), 850(6), ... (I'll call this list Q for ease of reference.) Some information: "greatest common factor" Let's look at 850(4) and 850(6). The number, 850 isn't the GREATEST common factor because 2 is a common factor to 4 and 6. These numbers can be rewritten at 1700(2) and 1700(3), respectively. This requirement means that we can eliminate some of the numbers from this list: 850(multiples of 2, except 2 itself) 850(multiples of 3, except 3 itself) 850(multiples of 5, except 5 itself) and so on. What remains of list Q is 850(1), 850(2), 850(3), 850(5) ... where everything in the parentheses, other than 1 is a prime number. But this is some fairly advanced thinking, your daughter may not be ready for this. If she is, GREAT! Back to the problem... List Q: 850(1), 850(2), 850(3), 850(4), 850(5), 850(6), ... The problem asks for two numbers where (1) 850 is the GCF, (2) one is not divisible by the other, and (3)they be the smallest numbers. Ask your daughter to choose two numbers from the list and make sure the pair she chooses satisfies all three conditions. Suppose we choose 850(1) and 850(2). Condition 1 is met. Condition 2 IS NOT met. 850(2) divided by 850(1) is a whole number. Therefore, these two numbers don't work. Choose another pair of numbers. Hope this is helpful. Jeanne, for the Teacher2Teacher service
Post a reply to this message

[Privacy Policy] [Terms of Use]
Math Forum Home 
The Math Library 
Quick Reference 
Math Forum Search