# Subtraction of Units of Length

## Students` Learning Outcomes

• Subtract measures of length in same units with and without borrowing.
• Solve real life problems involving same units of length for subtraction with and without carrying.

### Information for Teachers

• Question should be written vertically under column headings (km, m, and cm).

• Write large value in upper row and small value in bottom now.
• To find the difference of lengths, centimeters are subtracted from centimeters, meters from meters and kilometers from kilometers.

• If one of the columns has a smaller number on top, the number borrows from the number to its left.

• While teaching the lesson, also consult textbook where and when applicable.

### Material / Resources

Writing board, chalk/marker, duster, paper strips` chart (Relation of the nits and subunits of length)

### Introduction

• If a string is 5 meter long and someone cut 3 meter out of it. What length of the string is left now? (2cm)
• Ali`s height is 1m 23cm and his father’s height is 1m 86cm. how much father is taller than Ali? (63cm)

### Development

Activity 1

• Write the following statement on the board.

• Ask following questions from the students and write their answers on board.
• What is the length of pencil before sharpening? (14cm)
• How much length is reduced ?(2cm)
• Which operation can be used to find the new length of the pencil? (subtraction)
• Demonstrate how to solve this problem.

• Write another statement on board.

• Ask one of the students, what is the total distance? (14cm 149m)
• Ask the students to write 4km 149m on board under column headings (km and m)
• Ask another student, how much distance does Hassan travel by bus? (3km 218m)
• Ask the student to write 3km 218m under the first value.
• Ask another student, which operation can be performed to find the distance covered on foot? (subtraction)

• Explain it to the students, subtraction of units of length is same as the subtraction of whole numbers.

Activity 2

• Write the question of subtraction of some lengths with and without borrowing, on both sides of paper strips.
• Distribute paper strips to all students.
• Ask students to solve the given questions.
• Take a round in a class and observe their work.
• Guide them where necessary.
• Call volunteer students to share them work on board with the whole class.

### Sum up / Conclusion

• Conclude that:
• To find the difference between the lengths of two different objects, centimeters are subtracted from centimeters, meters from meters and kilometers from kilometers.
• When we borrow 1km from kilometers column, it is equal to 1000m and add 1000m into the meters column.
• When we borrow 1m from meters column, it is equal to 100cm and add 100cm into the centimeters column.

### Assessment

• Ask the students to solve the following questions.