Second Term Lesson Note for Week Seven
Class : Primary 3
Subject : Mathematics
Topic : Open Sentences
Duration : 80 minutes
Period : Double Periods
Reference Book :
- New Method Mathematics for Primary Schools ,Book 3 by Oredugba C. F. etal .
- Lagos State Unified Schemes of Work for Primary Schools (Primary 1 – 3).
- Online Resources
Instructional Material : Chart showing number sentences with unknown.
Learning Objectives : By the end of the lesson learners will be able to :
i. Find the unknown in addition and subtraction of number sentences;
ii. Find the unknown in multiplication and division of number sentences
iii. Solve word problems involving number sentences.
Previous Knowledge : Learners are familiar with addition, subtraction, multiplication and division of numbers.
Content :
An open sentence is the use of symbol to represent an unknown in any given arithmetic operation.
For examples :
1. 26 + [ ] = 39
2. [ ] – 12 = 23
3. 7 × [ ] = 28
4. [ ] × 5 = 40
5. [ ] ÷ 6 = 11
6. 36 ÷ [ ] = 12
A. In open sentences if 24 + [ ] = 54. The sentence can be interpreted as ‘ what number do I add to 24 to get 54.
B. If [ ] – 22 = 33, find [ ]. The sentence [ ] – 22 = 33 can be interpreted as ‘ if I subtract 22 from a number, the answer is 33. Then [ ] = 33 + 22.
Therefore, [ ] = 55.
This means when subtracting and the unknown Comes first in the number sentence. Then you will add the other number and the answer together to get the unknown.
C. If 5 × [ ] = 20, find [ ].
The sentence 5 × [ ] = 20 can be interpreted as ‘ What number do I multiply by 5 to get 20?’ 20 divided by 5 gives 4 or 5 × 4 = 20.
Hence, 5 × [ ] = 5 × 4. Therefore, [ ] = 4.
D. If [ ] ÷ 4 = 11, find [ ].
The sentence [ ] ÷ 4 = 11 can be interpreted as ‘What can be divided by 4 to get 11? Then we can say that 11 × 4 = 44. Therefore, [ ] = 44.
Presentation Steps :
Step 1 : Revision of the previous topic with the learners.
Step 2 : Introduces the new topic by explaining number sentence and open sentences with examples.
Step 3 : The teacher explains by solving open sentences on addition and subtraction of numbers using several examples.
Step 4 : He / she then explains further by interpreting the open sentences on multiplication and division of number with examples.
Evaluation :
Solve the following by finding the unknown.
1. 51 + [ ] = 63
2. [ ] + 39 = 79
3. 63 – [ ] = 15
4. [ ] – 19 = 64
5. 6 × [ ] = 48
6. 80 ÷ [ ] = 10
7. [ ] ÷ 5 = 6
8. [ ] × 6 = 54
Conclusion : At the end of the lesson learners were able to solve the problems given. The teacher then makes some corrections.
Assignment:
Find the missing number in each of the following.
1. 33 + [ ] = 57
2. [ ] + 18 = 45
3. 68 – [ ] = 40
4. [ ] – 43 = 36
5. 10 × [ ] = 70
6. [ ] × 12 = 72
7. 90 ÷ [ ] = 9
8. [ ] ÷ 5 = 11