[Numeracy 138] Re: Teaching Fractions etc...

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Carol King cking at lyon.k12.nv.us
Wed Feb 10 21:01:11 EST 2010

Teaching least common denominator when multiplication skills are lacking
is also an issue. It is not quick or obvious what that number would be
and students become quickly discouraged by the amount of work it takes.

If a student does not understand fractions I tend to teach it as the
numerator represents the number of pieces I have and the denominator
represents the number of pieces I need to make one whole item. We use
the tables in the room as an example: The table has 4 parts, so 4/4
makes a table. If a leg is missing I have 3/4; I almost have a table.
Once they really get the relationship of the two numbers I find they
really begin to understand the fractions.
Carol King
Fernley Adult Education
Fernley, Nevada
shiomha at lyon.k12.us

-----Original Message-----
From: numeracy-bounces at nifl.gov [mailto:numeracy-bounces at nifl.gov] On
Behalf Of Susan Jones
Sent: Wednesday, February 10, 2010 5:39 AM
To: The Math and Numeracy Discussion List
Subject: [Numeracy 135] Re: Teaching Fractions etc...

Fractions are an area I think there's a whole lot of potential for
bridging that cognitive breach between "real life thinking" and the
fearful math problems.

I did a little Camtasia presesntation with fractions - the only problem
is that there's this little teeny typo so, if I remember right, it says
boldly that 1/4 is greater than 1/2. While I was ecstatic that the
seriously struggling student I was showing it to took one look and said
"That ain't right!!" ... I havent' had time to go back and reconstruct
(can't find the original powerpoint I recorded).

However, one thing I did learn from delving into what other people have
done: the absolute necessity of teaching the *least* common denominator
is questionable if students are still developing the fraction concept.

Prime factorization is, absolutely, an invaluable skill set and an
awfully good foundation for lots of algebra. However, if students are
still wrestling with the concept of division and divisibility, then
comprehension is going to be limited. If students are still trying to
figure out fractions and why they need a common denominator at all, then
I find throwing prime factorization into the mix pretty much puts the
concepts in a blender and fragments them. I found that the state of
California agrees with me.

My thinking is that some time spent building the division and
divisibility concepts before leaping into fractions is one way to bridge
the concrete-abstract chasm. But that's my next email...

Susan Jones
Academic Development Specialist
Center for Academic Success
Parkland College
Champaign, IL 61821
sujones at parkland.edu

>>> Maureen Carro <mcarro at lmi.net> 2/9/2010 2:20 PM >>>

On Feb 8, 2010, at 6:16 PM, George Demetrion wrote:


> This brings up to my mind the importance of:

> Sequencing skill development from basic to more advanced

> Maximum possible simplicity as a critical scaffolding strategy in

> its own right

> Incorporating mathematical meaning making and inquiry as a critical

> part of the ongoing work

> Individual and collaborative scaffolding

> Sequencing skill development from basic to more advanced

This IS the essence of it all! When teaching math concepts, it is
important to do a "task analysis" to determine what the student needs
to have already mastered before proceeding with the instruction. This
applies to all instruction.

1.So many students trip up on fractions simply because they do not
have "fluid recall" of multiplication/division facts. This is
necessary for finding the "factors...including GCF", and
"multiples...including LCM", and "common denominators...including LCD"
in order to add or subtract fractions, and in the end, simplify
(reduce) answers to lowest terms. There is a constant mental
manipulation of multiplication/division facts. Sorry.... but "finger
tricks" and multiplication charts..... etc are a huge distraction to
the fluid mental thought process necessary to carry out all the steps
of fraction algorithms. We practice math facts as part of our "warm
up skills drill"... until most know the facts fluently. They need to
become mental... with " fingers and tricks" used "only as a last
resort crutch" when fatigue sets in.

2. Of course they need to know addition and subtraction facts as well.

What else do they need to know?

3. Prime numbers.... if you talk about "prime factorization" to
determine LCM and thus LCD, they need to know what prime numbers are.
These come in handy to recognize lowest terms fractions.... ie, we
know 3/5 is in lowest terms because they are both prime numbers.....
the only common factor being 1. I use a 100's chart and do the
"Sieve of Eratosthenes" to learn the prime numbers up to 100 ( I have
included this at the end).
Eventually when this is part of a "warm up skill drill"...... the
students instantly recognize prime numbers.

4. Fluid execution of short division: with larger fractions, or
improper fractions, one needs to do short or mental division in order
to simplify answers. I find most students never heard of "short
division" . When I show them and we practice, they are eternally
grateful! We do 2 or 3 short division problems as part of our "warm
up skills drill".

5. Rules of divisibility help as well. As part of a "warm up skills
drill", I might dictate a number and ask if it is evenly divisible by
3, or 6... Most students can tell if it is divisible by 2, 5, and 10 ,
but there are more.

Here is the Sieve of Eratosthenes:

The Sieve of Eratosthenes
Eratosthenes (275-194 B.C., Greece) devised a 'sieve' to discover
prime numbers. A sieve is like a strainer that you use to drain
spaghetti when it is done cooking. The water drains out, leaving your
spaghetti behind. Eratosthenes's sieve drains out composite numbers
and leaves prime numbers behind.
To use the sieve of Eratosthenes to find the prime numbers up to 100,
make a chart of the first one hundred positive integers (1-100):

1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100

Cross out 1, because it is not prime.

Circle 2, because it is the smallest positive even prime. Now cross
out every multiple of 2; in other words, cross out every second number.

Circle 3, the next prime. Then cross out all of the multiples of 3; in
other words, every third number. Some, like 6, may have already been
crossed out because they are multiples of 2.

Circle the next open number, 5. Now cross out all of the multiples of
5, or every 5th number.
Continue doing this until all the numbers through 100 have either been
circled or crossed out. You have just circled all the prime numbers
from 1 to 100!

> Maximum possible simplicity as a critical scaffolding strategy in

> its own right

> Incorporating mathematical meaning making and inquiry as a critical

> part of the ongoing work

Using everyday examples to develop fraction concepts, especially
bridging the concept that a fraction is a division problem. ( If we
divide 1 candy bar evenly between two people, how much does each one
get?) I write 1/2 as I state this simple scenario. What I have
written is the answer....1/2.

Thanks to others who have offered some fine examples of this as

> Individual and collaborative scaffolding

Absolutely.... students should contribute as to what to include in
"warm up drills".....for example.... eventually some things are no
longer needed, and others emerge! For success in higher math, there
is a huge knowledge base that builds, must be retained, and trained to

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