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OCR for page 154
1 ~ t-
. -
1. Topic of the lesson: division by two-digit numbers.
The first lesson out of nine lessons in the unit "Division".)
2. A plan for the entire unit (nine lessons)
(~) Regularities of divisions (two lessons)
Methods to find the answer to expressions like "128 . 16" (this lesson).
Divisions by "tens" and by "hundreds."
(2) Division by a two-digit number (six lessons).
Dividing by a two-digit number.
How to check the results of divisions.
Division by a two-digit number that needs an adjustment of a supposed quotient.
Stan(lar(1 algorithm for "(three-(ligit) . (two-(ligit)."
(3) Summing up the unit (assessment) (two lessons).
3. Objectives of the lesson
Fin(ling the methods to get the answer to the (livision "128 . 16" by students
themselves.
- Understanding the regularities of divisions such as, '~he answer remains the
same when we divide both the divisor and dividend by the same number" or
"By making a (livisor half, the answer becomes (louble."
4. Development of the lesson
OCR for page 155
Main Learning Anticipated Remarks on
Activities Students' Responses Teaching
Posing today's · presenting a · drawing a figure of the problem situation · talk about the previous
problem problem; class activity of planting
· the expression for getting the answer is bulbs on the school
'We are going to "128 - 16/' ground
plant 128 bulbs of · show a picture and
tulips into 16 · using a number line model to the students
planters. The same · If neeclecl, ask questions
number of bulbs to those students who
are to be planted could not understand the
in each planter. problem well;
How many bulbs · what is the unknown?
will be planted in · can you clraw a figure?
each planter?" · what if we change the
numbers in the
problem?
Students' · finclingoutthe way (0) By guessing · givehintstothose
problem to get the answer to (1 ~ By thinking how many "16s/' are there in 128 ? students who can not
solving on their the expression 128 - 16 - 16 - 16 - = 0 find a solution
own 128 - 16 (a repeated subtraction)
(2) By substituting numbers into the expression
At x 16 =128 by turns, we can get the answer.
1 x 16 = 16,2 x 16 = 32,
3x16=8,... 8x16= 128
(3) "Divicling by 16/' means cliviclecl first by 8,
anclthenLy2.
128- 16= 128-~8x21=~128-81-2=
16-2=8
(~) Divicling both cliviclencl and divisor by the
same number like 2 or A.
128- 16=~128-21-~16-21=6A -8=8
(5) When the divisor is multiplied by 2, the
quotient becomes half; 128 - 2 = 6A,
128 - ~ = 32.
So, we can get the answer of 128 - 16 as a
half of 128 - 8
APPE N DIX D
· ask the students to
explain how and why
the methods do work
· request another method
for those students who
got one method
OCR for page 156
Main Learning Anticipated Remarks on
Activities Students' Responses Teaching
Whole-class · presenting the ideas Focus on the following ideas to integrate the · pick a naive method like
discussion you came up with stuclents' methocls. guessing first
and listen to the · by estimating the number, find the number that
other stuclents' ideas applies to the equation; using 1` x 16 = 16 x 1` · focus on the regularities
Repeated subtraction falls into this iclea) of division
· comparing the · thinking by two steps
methods presented · using multiplication table, applying the
to find the regularity (If we make the number of planters
connections half, the number of bulbs also becomes half)
among them
· which method
might be more
effective?
Summing up · reflecting on the · when we clivicle both the cliviclencl and divisor
regularities of by the same number, the answer remains the
division we found same
· so, we can get the answer to division by a two-
cligit number, in certain cases, by reducing it
into division by a one-digit number
Applications · try the other cases
divisions by 12 or
18, by applying the so on
regularities
· 96 - 1 2 = (96 - 2) - (1 2 - 2) = AS - 6
· 96 - 12 = (96 - 3) - (12 - 31 = 32 - ~ and
· give such expressions
like96- 120r
1~- 18as
examples
APPE N DIX D
Representative terms from entire chapter:
main learning
