# Subtraction of Units of Mass/Weight

## Students` Learning Outcomes

• Subtract measures of mass/weight in same units with and without borrowing.
• Solve real life problems involving same units of mass/weight for subtraction with and without borrowing. ### Information for Teachers

• Write the values vertically under column headings (g and kg)
• Large value in upper row and small value in bottom row.
• To find the difference of weights, grams are subtracted from grams and kilograms from kilograms.
• If the grams column has a smaller number on top, the numbers on top borrows from the number to its left then adds into it, then find the difference. 1kg = 1000g • Repeat the key words for subtraction, how much left, reduced, lighter, heavier, how much etc.
• While teaching the lesson, also consult textbook where and when applicable.

### Material / Resources

Writing board, chalk/marker, duster, pointer/stick, balance, weights and weight textbook

### Introduction

• A bar of chocolate weighs 100g. Abu eats 40g. How much is left? • In May, Sameer weighed 52kg. In June, his weight had reduced to 48kg. How much weight did he lose? ### Development

Activity 1

• Write the statement on board.
• At a construction site there was 350kg 950g of sand. If there are 49kg 375g of sand is used in a material. How much sand is left? • Ask the following questions to the students:
• What was the total weight of sand? (350kg950g)
• How much sand was used in material? 49kg375g)
• How we find the remaining weight of sand? (by construction)
• Write their response on the board. • Ask them to solve it.
• Subtract grams from grams, as such; 950g – 378g = 675g.
• Now subtract “kg” from “kg”, as such; 350kg – 49kg = 301kg, hence, the remaining weight of sand is 301kg675g.
• Write another statement on the board. • Ask the following questions to the students.
• What was Ali`s weight with shoes? (45kg15g)
• What was the weight of shoes? (1kg150g)
• Which operation will we use to find the actual weight of Ali?(Subtraction)
• Write their responses on board under the heading of units(kg and g) • Ask one student to solve it on the board.
• Ask them how we subtract 150g from 15g? (we borrow 1kg from 5kg)
• How many grams are there in 1kg?(1000g)
• Now how many grams we have? (1018g) • Hence, actual weight of Ali is 43kg 868g.

### Activity 2

• Ask students to solve the following sums in their notebook. • Tell them, firstly subtract grams from grams.
• Tell them, if the grams column has a smaller number on top, the numbers on top borrows from the number to its left then adds into it, then find the difference. 1kg = 1000g
• Observe their work and guide them where necessary.
• Revise the relation between “g” and “kg” by asking from the students.

### Sum up / Conclusion

• Conclude that:
• To find the difference of weights, grams are subtracted from grams and kilograms from kilograms.
• If the grams column has a smaller number on top, the numbers on top borrows from the number to its left then adds into it, then find the difference. 1kg =1000g

### Assessment

• Ask the following questions to the students;
• Which is the smaller unit of weight?
• Which unit is used to weigh heavier objects?
• Which mathematics operation is performed for finding the difference between the weights of two objects?