Second Term Lesson Note for Week Six
Class : Primary Four
Subject : Mathematics
Topic : Estimations (Rounding off numbers)
Duration : 80 Minutes
Period : Double Period
Reference Book :
New Method Mathematics for Primary Schools, Book 4, by Learn Africa.
Lagos State Unified schemes of work for Upper Primary School, Primary 4 – 6.
Online Resources
Instructional Material : Chart showing the rules of rounding off numbers.
Learning Objectives : By the end of the lesson learners will be able to :
i. Explain Estimation and rounding off numbers to the nearest 10, 100 and 1000.
ii. Estimation involving Addition and Subtraction of whole numbers and decimals.
iii. Estimation involving multiplication and division of Numbers.
iv. Solve word problems involving estimations.
Content :
Estimation ( Rounding off Numbers)
Rules for rounding off decimals to the nearest whole number
When the rounding off decimals to the nearest whole number, look at the digit in the tenths place.
If this digit is 5 or greater than 5, replace the digits after the decimal point by zero and add 1 to the digit in the units place
If this digit is less than 5, replace the digits after the decimal point by zero.
Note: ‘≈’ means ‘is approximately equal to’
ROUNDING WHOLE NUMBERS
Consider these numbers:
10 20 30 40 50 60 70 80 90
Each of these numbers are multiples of 10 and each number has zero in its unit place. These numbers (i.e. multiples of 10) are round numbers.
Consider these numbers:
11 12 13 14 15 16 17 18 19 21 24 25 etc
These numbers are called non-rounded because the digits in the unit place is greater than zero.
Non-rounded numbers can be replaced by the nearest multiples of 10, 100 and 1000. This is called rounding off numbers.
We can use the number line to round numbers to the nearest 10 and 100. We can also round without using the number line.
A. Rounding to the nearest 10
Examples
Round to the nearest 10.
1. 46 ≈ 50 (In 46, 6 is rounded up to 1 and then added to 4 tens to make 5 tens)
2. 22 ≈ 20 (In 22, 2 is rounded down to 0 and then added to 2 tens to make 2 tens)
B. Rounding to the nearest 100.
Examples
Round off to the nearest 100.
1. 616 ≈ 600 (
2. 870 ≈ 900 (
C. Rounding decimals to nearest whole numbers
Decimals can also be rounded to the nearest whole numbers with and without using a number line.
For Example : Round off the following decimal numbers to the nearest whole numbers.
6.7 ≈ 7 (to the nearest whole number)
6.3 ≈ 6 to the nearest whole number
17 ≈ 20 to the nearest tens
54.58 ≈ 54.6 (to the nearest tenths)
126.039 ≈ 126 (to the nearest whole number)
EXERCISE 1.
1. Write to the nearest whole number :
i. 4.7
ii. 1.1
iii. 17.9
iv. 8.36
v. 0.9
vi. 29.54
D. Round off to the nearest 100’s and write the estimated answers and correct answer.
1. 424 + 132
≈ 400 + 100
≈ 500 (500 is the Estimated value, but 556 is the Actual value. )
2. 675 – 401
≈ 700 – 400
≈ 300. (300 is the Estimated value, but 274 is the Actual value. )
Evaluation :
1.Round off to the nearest 100’s and write the estimated answers and correct answer.
| Given values | Estimated values | Actual values |
| 1. 537 + 261 | ||
| 2. 456 – 324 | ||
| 3. 541 + 302 | ||
| 4. 437 – 398 | ||
| 5. 323 + 212 |
2. Round of the given number to their :
i. Nearest 10’s ii. Nearest 100’s
a. 576 ≈ ___________ __________
b. 830 ≈ ___________ __________
c. 445 ≈ ___________ __________
d. 709 ≈ ___________ __________
Conclusion : At the end of the lesson learners were able to answer the questions correctly.