Explanation:
Here's an activity that would be great for your third graders! Not only does it offer variety from traditional subtraction problems, but it encourages higher level thinking while incorporating technology. (1)This activity is generative in nature, which means that students will perform the task assigned, coming up with a wide range of correct solutions. (2) Before you use this activity in your classroom, it is a good idea that students have experience with multiple digit subtraction.
In your classroom, the students will use calculators to search for combinations of numbers. These combinations, when subtracted, will result in a difference that has already been assigned by the teacher. It is important to begin with a simple lead-in activity in order to get the idea across.
You may start with a pair of dice. Begin by saying, "I want you to watch carefully as I roll the dice. Each time I roll, I am going to subtract my two numbers. I am looking for a difference of two. So I will keep rolling the dice until I have I can subtract and get the number two. There are several ways, so be thinking in your mind what different combinations I could roll." It shouldn't take long at all to roll a 6/4, 5/3, 4/2, or 3/1. Write the numbers down for the children to see. Keep going and don't stop at just one solution. Find at least one other, and ask students if there are any different combinations they thought of.
Now you can give students a little time to practice with dice. Have them work with partners, and give each pair two dice. Make it more challenging by giving them dice that go up to eight or ten. Give them a difference to shoot for (maybe three or four) and a few minutes to roll and come up with different combinations of numbers that will yield the assigned difference.
It's time to get started using the calculators. Before you pass out the calculators, explain what is expected from the students. When they rolled the dice, they were looking for combinations that yielded a certain difference. Now they will do the same thing with calculators. The students will be given the attached handout to fill in. The hand-out starts off easy, and progressively gets more challenging. It adds rules and constraints requiring the students to think a bit more, making generalizations as they go along.
This may be very easy for some students,
yet challenging for others. (5,6) After they have completed the worksheet,
you can lead a discussion by asking them what they noticed about even and
odd differences. What types of short-cuts did they use? This will lead to
an insightful discussion, where you can discuss things that students observed
for the first time during this lesson. (13) Consider following this lesson
with one on properties of addition and subtraction facts.
Here's the Difference!
Use your calculator to come
up with 5 ways to subtract and get a difference of 10.
-
= 10 
-
= 10
-
= 10 
-
= 10
-
= 10
Use your calculator to come
up with 5 ways to subtract and get a difference of 25.
-
= 25
-
= 25 *
At least one of your numbers must be greater than 1000.
-
= 25
-
= 25 *
At least one of your numbers must be even.
-
= 25
Use your calculator to come
up with 5 ways to subtract and get a difference of 112.
-
= 112 *
At least one of your numbers must be between 120- 135.
-
= 112
* At least one of your numbers must be greater than 500.
-
= 112
-
= 112 *
At least one of your numbers must be odd.
-
= 112
Use your calculator to come
up with 5 ways to subtract and get a difference of 5.5
-
= 5.5 *
Use "10" as one of your numbers.
-
= 5.5
* At least one of your numbers must be greater than 5500.
-
= 5.5 *
At least one of your numbers must be even.
-
= 5.5 *
At least one of your numbers must be odd.
-
= 5.5
*At least one of your numbers must have three digits.
Here's the Difference!
Lesson Plan
Intended for grade level:
3
Area of math engaged: subtraction
Specific idea:
inferences about multiple digit subtraction using calculators
(9) Materials Needed: 2 dice for teacher, 2 dice for each pair of students
pencil and scrap sheet for each student
calculator for each learner
attached worksheet for each student
Anticipatory Set:
"I have seen how much all of
you enjoy using calculators, and how well you can subtract. Today we are
going to use calculators to hunt for numbers. We are on a hunt for numbers
that will give us a certain difference when we subtract them."
Behavioral Objective:
The learner will be able to utilize
a calculator as a tool to experiment and come up with several subtraction
facts that will yield preassigned differences.
Instructional Input:
"I will begin with a pair of
dice. I am going to roll my dice and subtract the two numbers that I roll.
I am looking for a difference of two. So I will continue to roll the dice
until I roll a combination that will give us a difference of two. Help me
subtract out loud as I roll and help me find a difference of two."
When the teacher rolls a combination that yields a difference of two, she
will write the subtraction fact for all the students to see. She will ask
students if there are other possible combinations. With their affirmation,
she will roll until she finds another combination that provides a difference
of two. After she has two subtraction facts written for all the students
to see, she will ask the students what other combinations would have resulted
in a difference of two. The teacher will write each correct combination.
Guided Practice:
The students will perform a similar
task in pairs. Each pair of students will have a pair of dice. To make it
more challenging, students may use dice with eight or ten sides. Assign
each pair of learners a certain difference(such as three or four), and have
them roll their dice until they come up with at least two correct subtraction
facts. Then allow them to stop rolling, and provide the other correct combinations.
As they go, have students make an exhaustive list that includes all combinations
yielding their particular difference. This should only take a few minutes.
Afterward, call on groups to share their findings. The share time will be
more interesting if each groups is assigned varying differences.
Independent Practice:
Have each student use a calculator
to complete the worksheet provided with this lesson plan. Tell them not
to "shoot for numbers in the dark," but to try and look for short-cuts.
They should make observations about even and odd numbers, and how to come
up with solutions when they are given constraints.
Closing:
The teacher asks students what things
they have noticed while working on this lesson. Lead the discussion by asking
what an (even # - even#) equals. How about an (odd# - even #), and vice
versa? (7,8) Students will recognize that (E - E = E); (O - O = E); (E -
O = O); and (O - E = O). Ask students what short cuts they noticed. They
will tell you they added the difference to another number to come up with
the third number. Ask what else they noticed, and you may be surprised what
an interesting discussion results!