Second Term Lesson Note for Week Two
Class : Primary Five
Subject : Mathematics
Topic : Estimations (Rounding off numbers)
Duration : 80 minutes
Period : Double Periods
Reference Book :
- New Method Mathematics for Primary Schools, Book 5 by Learn Africa
- Lagos State Unified Schemes of Work for Primary Schools (Primary 4 – 6)
- Online Resources
Instructional Material : Charts showing rounding up of numbers using place values and significant figures
Learning Objectives : By the end of the lesson, learners will be able to :
i. Explain Rounding off numbers.
ii. Round off numbers to the nearest tens, hundreds and thousands.
iii. Estimate sums, differences and products of numbers.
Previous Knowledge : Learners have been taught addition and subtraction on a number line.
Content:
Estimation is the approximation of a number by rounding it up to the nearest tens, hundreds, or thousands depending on the value stated as required.
In rounding off numbers, we either round a number by using the place value or significant figures.
When rounding off numbers, we either round up or round down numbers.
a.) Rounding up numbers : Numbers from 5 to 9 are rounded up to ‘1’, and then added to the next immediate number stated by the values.
b.) Rounding down numbers : Numbers from 0 to 4 are rounded down to ‘0’ , and then added to the next value stated by the instruction.
For examples:
Round off the following to the nearest tens, hundreds and thousands:
1.) 106 = 100 ( to the nearest hundreds)
106 = 110 ( to the nearest tens)
2.) 137 = 100 (to the nearest hundreds)
137 = 140 (to the nearest tens)
3.) 653 = 700 (to the nearest hundreds)
653 = 650 ( to the nearest tens)
4.) 7984 = 8000 (to the nearest thousands)
7984 = 8000 (to the nearest hundreds)
7984 = 7980 ( to the nearest tens)
Round off the folliwing to the nearest whole number:
1. 29.7 = 30 (to the nearest whole number)
2. 12.1 = 12 (to the nearest whole number)
3. 38.37 = 38 (to the nearest whole number)
4. 175. 816 = 176 (to the nearest whole number)
Rounding off to the nearest tenths, hundredths and thousandths.
i. 76.78 = 76.8 ( to nearest tenth)
ii. 9.426 = 9.43 (to the nearest hundredths)
iii. 123.7314 = 123.731 (to nearest thousandths)
Tenth is the first digit after the decimal point. It is the same as one decimal place.
Hundredths is the second digit after the decimal point. It is the same as two decimal places.
Thousandths is the third digit after the decimal point. It is the same as three decimal places.
Estimating Sums and Differences of values
1. 8.56 + 7.12 = 15. 68 (Actual /original value)
For estimated sums, we have :
8.56 ~ 9 and 7.12 ~ 7. Hence, the estimated sum is : 9 + 7 = 16
2. 4.586 – 1.254 = 3.332 (Actual/ Original value)
For estimated difference, we have :
4.586 ~ 5 and 1.254 ~ 1. Hence, the estimated difference is : 5 – 1 = 4
Difference = (Estimated result – Actual result)
Presentation Steps :
Step 1 : The teacher revises the previous topic with the learners by asking questions orally.
Step 2 : He/ she introduces the new topic by explaining the concept of rounding off numbers involving whole numbers and decimal numbers
Step 3 : He/ she solve several examples on rounding off numbers and calls the learners in turns to solve on the board for a clearer understanding thereby involving other to state if it is right or wrong. He/ she then, calls the learners to spot the errors made and correct them.
Step 4 : The teacher then explains the idea of estimations involving sums, differences and multiplication operations.
Evaluation : The teacher examines the learners to ascertain that the lesson is well understood by asking them to do the following questions.
1. Round off to the nearest :
i. Tens; ii. Hundreds; and iii. Thousands.
a. 1563 = b. 4106 = c. 9065 =
2. Round off to the nearest whole number :
a. 4.9 = b. 15.4 = c. 134.82 =
3. Round off the following to the nearest :
i. tenth ii. hundredths iii. thousandths
a. 28.3874 = b. 392.6871 =
Conclusion : At the end of the lesson, learners were able to solve the problems correctly while the teacher makes some corrections as he/ she moves around them in the class.
Assignment :
Find the Actual and the difference between the Actual and Estimated.
a. 89.43 + 90.65
b. 526.456 – 214.218
c. 6.24 × 12
d. 75.68 × 15
e. 9.63 + 4.82
f. 89.74 – 24.69