Estimation : Round up of numbers (Addition and Subtraction)

SECOND TERM E NOTES FOR PRIMARY 4 MATHEMATICS

SUBJECT: MATHEMATICS
CLASS: BASIC FOUR / PRIMARY 4
WEEK: 6
TOPICS: Estimation: Round-up of numbers (Addition and Subtraction)

Importance:

• It is used in budget writing.
• To estimate the total cost of items at a departmental store.

Learning Objectives:

Pupils should be able to:

• Identify actual numbers.
• Solve round-up numbers.
• Calculate addition and subtraction of round-up numbers.
• Interpret and solve real-life problems on estimation.
• Solve quantitative reasoning.

Learning Activities:

• Pupils in a group fill an empty jar with pebbles, count the number of pebbles that will fill the jar, then estimate the number.
• Pupils use a ruler and cardboard to prepare a scale chart for estimation.

Embedded Core Skills:

• Critical thinking and problem-solving skills
• Communication and Collaboration
• Leadership skills and Personal Development
• Creativity and Imagination

Audio Resources:

• Empty jar
• Pebbles
• Hands

Content:

Estimation is a way to make a guess about a number that is close to the actual answer. It can help you do math problems faster, and it can also help you check if your answer is reasonable.

One way to estimate is to round numbers up or down. When you round a number, you change it to the nearest multiple of 10, 100, 1000, and so on. Here are some examples:

Rounding up for addition:

Suppose you want to add 46 and 22. To estimate the answer, you can round up both numbers to the nearest ten:

• 46 rounds to 50
• 22 rounds to 20 Then, add the rounded numbers:
  50 + 20 = 70
  This is an estimate of the answer. The actual answer is 68, so your estimate is a little bit higher.

Rounding up for subtraction:

Suppose you want to subtract 28 from 49. To estimate the answer, you can round up both numbers to the nearest ten:

• 49 rounds to 50
• 28 rounds to 30 Then, subtract the rounded numbers:
  50 – 30 = 20
  This is an estimate of the answer. The actual answer is 21, so your estimate is a little bit lower.

Remember, estimation is not always exact, but it can help you get a sense of what the answer should be.

To use empty jars and pebbles for estimation, follow these steps:

1. Start by pouring some pebbles into an empty jar and count how many pebbles there are. For example, if you count 32 pebbles, you can round this number to the nearest ten (40).
2. Now take another jar with some pebbles, let’s say you count 17 pebbles. You can round this number to the nearest ten (10).
3. Add the rounded numbers together:
   40 + 10 = 50
   This is an estimate of the answer.

To use your hands for estimation:

1. Hold up both of your hands and count how many fingers you have. For example, 8 fingers on one hand and 7 fingers on the other hand gives you 15 fingers.
2. You can round this to the nearest ten by rounding up to 20.
3. Now suppose you want to subtract 4. You can estimate by rounding 4 down to 0, and subtracting from the rounded number:
   20 – 0 = 20
   This is an estimate of the answer.

Remember, estimation is not always exact, but it can give you a good idea of the answer!

ESTIMATION

Rules for rounding off decimals to the nearest whole number:

• When 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 has zero in its unit place. These are round numbers.

Consider these numbers:
11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 24, 25
These are non-rounded numbers because the digits in the unit place are greater than zero.

Non-rounded numbers can be replaced by the nearest multiples of 10 or 100. This is called rounding.

We can use a number line to round numbers to the nearest 10 and 100, or round without using the number line.

Rounding to the nearest 10:

Examples:

• Round 46 to the nearest 10 → 50
• Round 22 to the nearest 10 → 20

Rounding decimals to the nearest whole number:

Decimals can also be rounded to the nearest whole numbers, with or without using a number line.

Examples:

• Round 6.7 to the nearest whole number → 7
• Round 6.3 to the nearest whole number → 6
• Round 17 to the nearest ten → 20

EXERCISE 1:

Write to the nearest whole number:

1. 4.7
2. 1.1
3. 7.9
4. 8.6
5. 0.9
6. 13.2

Evaluation Questions:

1. What is the rounded-up estimate of 53 + 27?
   a) 60
   b) 70
   c) 80
   d) 90
2. What is the rounded-up estimate of 198 + 74?
   a) 260
   b) 270
   c) 280
   d) 290
3. What is the rounded-down estimate of 492 – 223?
   a) 200
   b) 250
   c) 270
   d) 300
4. What is the rounded-down estimate of 837 – 453?
   a) 300
   b) 350
   c) 380
   d) 400
5. What is the rounded-up estimate of 99 + 28?
   a) 110
   b) 120
   c) 130
   d) 140
6. What is the rounded-up estimate of 67 + 44?
   a) 100
   b) 110
   c) 120
   d) 130
7. What is the rounded-down estimate of 745 – 568?
   a) 100
   b) 150
   c) 170
   d) 200
8. What is the rounded-down estimate of 933 – 671?
   a) 200
   b) 250
   c) 260
   d) 300
9. What is the rounded-up estimate of 348 + 198?
   a) 500
   b) 540
   c) 580
   d) 620
10. What is the rounded-down estimate of 576 – 238?
    a) 200
    b) 250
    c) 270
    d) 300

Lesson Presentation

Introduction:

1. Begin by asking students if they’ve ever had to make a guess about how many objects are in a jar or container.
2. Explain that today, we’ll be learning about a way to make educated guesses, or estimates, when we do math problems.
3. Define estimation as making a guess about a number that is close to the actual answer.
4. Explain that we’ll focus on rounding up numbers to the nearest ten to make estimation easier.

Body:

1. Write the numbers 27 and 44 on the whiteboard.
2. Ask students to round each number to the nearest ten and record their answers.
3. Check student answers and review the process of rounding up to the nearest ten.
4. Write the problem 27 + 44 on the whiteboard.
5. Ask students to estimate the answer by rounding up each number to the nearest ten and adding.
6. Model how to solve the problem using this method.
7. Repeat the process with subtraction problems, using the same numbers.
8. Explain that we can also use empty jars and pebbles to estimate addition and subtraction problems.
9. Demonstrate how to use pebbles to round up and add or subtract numbers.
10. Ask students to try it on their own, using the empty jars and pebbles.
11. Explain that we can also use our hands to estimate addition and subtraction problems.
12. Model how to use hands to round up and add or subtract numbers.
13. Ask students to try it on their own, using their hands.

Conclusion:

1. Review the steps for rounding up to the nearest ten and using this skill to estimate addition and subtraction problems.
2. Ask students to share any questions they have or examples of how they might use this skill in everyday life.
3. Summarize the importance of estimation as a way to make math problems easier and more manageable.

Assessment:

• Students will be assessed on their participation in rounding numbers, their ability to estimate sums and differences, and their completion of the evaluation questions.

Conclusion:

1. Mark the exercise and provide feedback on students’ progress.
2. Answer any questions students may have.
3. Conclude with a summary of what has been learned and encourage students to practice estimating numbers.

SEO Title: Estimation: How to Round-up Numbers in Addition and Subtraction
Focus Keyphrase: Estimation, Round-up numbers, Addition, Subtraction
Slug: estimation-round-up-numbers-addition-subtraction
Meta Description: Learn how to estimate numbers by rounding up for addition and subtraction problems. This lesson covers estimation strategies and practical applications for Primary 4 students.