Technical Card in Mathematics
Grade 2 Title: Subtraction Duration: 1 period
Introduction
In grade one, children learn the concept and the techniques of addition, while the subtraction has been introduced in as an independent operation from addition. In this lesson, they will learn the relation between addition and subtraction, and this relation facilitates the solving of certain problems situations that relate the part to the whole.
Prior knowledge
Before starting this lesson, make sure that students:
 Know what is meant by left and right.
 Can count the number of objects less than 20
 Can write an addition sentence.
Lesson objectives
By the end of this lesson, students will be able to:
 Write the subtraction sentence modeled by a pan balance
 Write the subtraction sentence related to a given addition situation
Materials
Preferred materials 
Pan Balance 
Colored shapes 
Overhead projector 
Alternative materials 
Pan Balance 
Beads,cereals (bean,chick peas,..) 
Worksheets 
Testing the prior knowledge [510 min]
Give each pair of students a copy of sheet 1, and ask them to do it within 5 minutes.
Make sure that each student distinguish between left and right, and can write an addition sentence; if some students can’t do that, then spend 5 to 10 min to teach them these concepts.
Activity (concrete stage) [15 min]
Display a pan balance and review with the students how it operates, then asks a volunteer to place some cubes in both pans of the balance (figure 1), then ask:
 Which pan is lighter? [ have children point on the lighter pan, in this case the right pan]
 How many connecting cubes are needed on the lighter pan to make balance? [ the answer is the blank in the equality 7 + ___ = 11]
 Who can write the addition sentence? [ 7 + 4 = 11]
 Subtract 117=____.
Ask another volunteer to place some shapes in both pans of the balance (figure 2), then ask:
 Which pan is heavier? [ Have children point to the heavier pan, in this case the right pan]
 How many triangles do we need to take away from the heavier pan to make balance? [ the answer is 3]
 Who can write the subtraction sentence? [ 93=6]
Instructions
In the first experiment of the activity, we introduce the concept "additive equalities with blank", of the type
a + ___= b, [ in this case 7+ ___ = 11]
While doing this part of the activity, draw the situation on the board as shown in (figure 3).
In the second experiment of the activity, we introduce the concept of subtraction "take away to make balance"
While doing this part of the activity, draw the situation on the board as shown in (figure 4).
Drill (semi concrete stage) [10 min]
Give each pair of students a copy of Sheet 2, and ask them to do it within 5 minutes.
While students solving the worksheet, move between them and write some notes about students work using Sheet 3.
Ask some volunteers to talk about their sheets, and then represent some situations on the board.
Exercises (Abstract stage) [15 min]
Give each student a copy of Sheet 4, and ask him/her to:
 Do it within 5 minutes. [Think].
 Compare the solution with his/her partner. [ Pair]
 Discuss the solution with the whole class. [Share]
Reflection [5 min]
Ask some reflection questions:
 How would you explain to a younger child how to make the sides balanced?
 How could you use the balance to complete the number sentence?
Sheet 1
Sheet 2
Sheet 3
# 
Name 
Comments 
1 


2 


3 


… 


Sheet 4
1. Complete the following sentences
12 + 15 = ....... 
18 ...... = 14 
20  ...... = 2 
10 + ...... = 19 
9 + ...... = 14 
18  ...... = 14 
20  ...... = 10 
10  ...... = 1 
9 + ...... = 19 
18  ...... = 9 
20  ...... = 3 
10 + ...... = 10 
2. Subtract
199 = ـــــــ 
181 = ـــــــ 
137 = ـــــــ 
1810 = ـــــــ 
203 = ـــــــ 
135 = ـــــــ 
106 = ـــــــ 
2010 = ـــــــ 
208 = ـــــــ 
145 = ـــــــ 
116 = ـــــــ 
1710 = ـــــــ 