[Numeracy 121] Re: introductions

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Carolyn Dickinson dickins2 at wncc.net
Mon Feb 8 18:18:30 EST 2010


What is the difference between the Lowest (or least) Common Denominator and
the Least Common Multiple and what different functions do they accomplish?

The LCD is the smallest number that will go INTO each of the numbers, while
the LCM is the smallest number that each of the numbers will divide into
(the smallest number that is a multiple of both numbers).

Suppose the numbers are 15 and 21. The LCD would be 3: 15 = 3 * 5; 21 = 3 *
7. The number they have *in common* is 3.
Suppose the numbers are 49 and 98. The LCD would be 49: 49 = 7 * 7; 98 = 7 *
7 * 2. The numbers they have *in common* are 7 and 7, and 7 * 7 = 49.

Try 45 and 21 for the LCM. What is the smallest number that is a multiple of
both numbers? 45 = 3 * 3 * 5, 21 = 3 * 7. The LCM = 3 * 3 * 5 * 7 or 105.
(Each number has a 3, so the first three only counts once. There is an extra
3 in 45, plus the 5. 21 still has a 7. Multiply all those together.
Or let's try 15 and 49. 15 = 3 * 5, 49 = 7 * 7. No numbers in common, so
multiply them all together. LCM = 3 * 5 * 7 * 7 or 735.

Does that help?

Carolyn Dickinson
Western Nebraska Community College
Scottsbluff, Nebraska

On Sat, Feb 6, 2010 at 12:56 PM, George Demetrion <gdemetrion at msn.com>wrote:


>

> Good afternoon all.

>

> While I am an experienced adult educator I am a newbie math teacher, but

> I'm plugging away in my first transitions to college basic math course.

>

> We've had two three hour sessions thus far in a 15 week course and things

> are moving along okay.

>

> To be sure I've put a lot of time practicing my math through basic algebra

> and concentrating on the assignments in our weekly sessions.

>

> I'm learning and I'm also getting a good experiential dose of math phobia,

> which in turn, in the process of transforming in the process of learning and

> then drawing on my overall teaching skills, especially incorporating basic

> explanation, a lot of practice and collaborative scaffolding instructional

> processes.

>

> One technical question:

>

> What is the difference between the Lowest (or least) Common Denominator and

> the Least Common Multiple and what different functions do they accomplish?

>

> Keep it simple and straightforward, please.

>

>

> George Demetrion

> East Hartford, CT

>

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