LESSON PLANNING OF ROUND OFF DECIMALS

LESSON PLANNING OF ROUND OFF DECIMALS

Subject Mathematics

Students` Learning Outcomes

• Round off decimals up to specified number of decimal places.

Information for teachers

• Round off decimal to the nearest whole number.

• o   To round off a decimal to the nearest whole number, we drop the part after the decimal point and write only the whole number.
• o   Follow the following steps;

Step 1: If the digit on the first decimal place is greater than or equal to 5, we add 1 to the whole number.

Step 2: If the digit at the first decimal place is less than 5, ‘1’ is not added to the whole number and written as it is.

Step 3: For example: 235.687 will change into 236[‘1’ has been added to 235 as 6>5], 235.587 will also change into 236 [‘1’ has been added to 235 as 5=5], 235.487 will change into 235[‘1’ has not been added to 235 as 4<5] round off decimal to the ‘1’ decimal place.

o   To round off a decimal to one decimal place, we consider the digit at the second decimal place.

Step 1: If it is less than 5, we simply write the given decimal up to ‘1’ decimal place and drop all the digits appearing after the first decimal place.

Step 2: If it is greater than or equal to 5, we add ‘1’ to the digit at the first decimal place and drop all the digits appearing after the first decimal place.

Step 3: For example: 78.63 will change into 78.6 [‘1’ has not been added to 6 as 3<5], 78.657 will change into 78.7 [‘1’ has been added to6 as 5=5], 78.687 will change into 78.7 [‘1’ has been added to 6 as 8>5] Round off decimal to the 2 or 3 decimal place.

o   To round off a decimal to 2 or 3 decimal place, we consider the digit at the hundredth or thousandth decimal place respectively.

o   If the digit on the hundredth or thousandth place is equal to or greater than ‘5’ then we add ‘1’ to the digit which we are rounding off and drop all the digits coming afterwards.

o   If the digit on the hundredth or thousandth place is less than ‘5’ then we simply write the digit which we are rounding off and drop all the digits coming afterwards.

Material / Resources

Writing board, chalk / marker, duster, textbook, large wooden scale, number cards

Introduction

• Ask students: Do you know, what is the rule of rounding of a number to the nearest, tens or hundreds place?
• Encourage them for the correct answer.
• Tell them that the rounding off of the decimals will follow the same rule.
• Draw a number line on the board from 0-1 and divide it into 10 equal parts.

• Tell them by drawing lines from 0.0 – 0.4 that it will be rounded off as ‘0’.
• Tell them by drawing lines from 0.5 – 1.0 that it will be rounded off as ‘1’.
• Explain all the steps of rounding off decimals as a whole number.
• Give example by underlining the digit after the decimal point:

56.7895               56.3895

57                        56

• Revise the concept of the place value of a decimal number and tenths, hundredth and thousandths.

Development

Activity 1

• Distribute the number cards in the class, one card per student.
• o   On one side of the card a decimal number should be written and on the other side a whole number should be written. (The white is one side of the card and dark is the other side of the same card)

o   One student will show the front side of his/her card with a decimal number. All the students will look at the back side of their cards for a rounded off whole number of the same decimal number.

o   This activity will continue till all the students will show cards to the class.

• Sum up the activity by revising the rule of changing the decimal number into the nearest whole number.

Activity 2

• Revise the steps of rounding off a decimal number into the nearest whole number.

• Give example: 65.347 will change into 65.3, whereas 65.365 will change into 65.4
• Divide the students into the groups of four.
• Ask them to write the steps of rounding off a big decimal number into a one place decimal number by looking at the examples written on the board.
• Take a group wise feedback.
• Encourage them for the correct answer.
• Write few decimal numbers on the board and ask the students to round each number off to one place of decimal by following the same ruler, used in the rounding off the decimal to the whole number.
• Take a round to help them for any inconvenience.
• Display the correctly done work in the class for the encouragement of the groups.

Activity 3

• Ask the students to write steps for rounding off a decimal number to two place of decimal and three place of decimal simultaneously.

• Take a whole class feedback.
• Write few questions on the board for them to solve individually.
• Ask students to swap their copies in pairs for cross checking.
• Ask them to correct their mistakes as pointed out by their peers.

Activity 4

• Write the following two decimal numbers on the board.

47.6735                39.381

• Call different students to round off these numbers on the board up to whole number, one place of decimal, two place of decimal and three place of decimal.
• Give them some questions from the textbook to do in their copies.
• Take a round to guide and help them while they will do their work.
• Collect their copies to check the work afterwards.

Sum up / Conclusion

• Rounding off a number is a step wise process.
• For rounding off a decimal number the place value of the digits should be revised.
• If a digit (that comes after the digit which is being rounded off) will be greater than or equal to ‘5’ then we add ‘1’ to the rounded off digit and drop all the next digits.
• If a digit (that comes after the digit which is being rounded off) will be less than ‘5’ then we write the number up till the rounded off digits as it is and drop all the next digits.

Assessment

• Give some questions from the textbook to solve.
• Complete the following grid rounding off the given decimal numbers to the nearest whole number.