# Addition and Subtraction of Units of Mass / weight

Lesson Planning of Addition and Subtraction of Units of Mass / weight

Subject Mathematics

Students` Learning Outcomes

• Add and subtract expressions involving similar units.
• Use appropriate units to measure weight of different objects.
• Solve real life problems with application of above two.

Information for Teachers

• Kilograms and grams are used to measure the weight of different objects.
• Kilograms are used to measure heavy objects whereas grams are used for lighter objects.
• Similar units can be added or subtracted only, if units are not similar, we make them similar before addition or subtraction.
• For adding grams into kilograms first we convert kilograms into grams and for this we multiply number of kilograms by 1000.
• During this lesson, the teacher should consult textbook at each level wherein and whenever it is required.

Material / Resources

Writing board, chalk/marker, duster, school bag, scale, pictures of almond, peanut, flour, rice, sugar and salt, textbook

Introduction

• Collect various objects that are easily available, as; toys, school bags, geometry box etc.
• Place the objects on a table along with a set of simple balances.
• Weigh these objects on balance and write on the board. “The geometry is lighter than school bag”.
• Put some more object on the geometry side and tell the students that now weight of both sides look same.
• Ask the students what do you think would be the weight of all toys.
• Take their feedback and tell them that it would be in kilograms
• Tell them that today we will learn about the application of “units of weight”.

Development

 Activity 1 Addition of the same units: Explain to the students that for adding grams into kilograms first we convert kilograms into grams and for this we multiply number of kilograms by 1000. Describe the following statement to the students: as; There are 80 g of almonds and 1 kg 13 g peanuts in a bag. Demonstrate on the board what will be the total weight of both dry fruits? Almonds            = 80g Peanuts              = 1 kg, 13 g Convert kg in g = [1 x 1000 + 13] g          = 1013 g. Total dry fruits  = 80 g         + 1013 g       = 1093 g. Reiterate that only same units can be added or subtracted.
 Activity 2 Subtraction of expressions involving similar units. Solve the following question on the board to teach how to subtract expressions involving similar units. Amana’s weight is 22 kg, while Zane’s weight is 19 kg. How much extra weight Amna has? Amana`s weight   =   22 kg Zane`s weight      =   19 kg Difference between their weights  =  [22 – 199 ] kg = 3 kg Explain the students that both weights are in kilograms (same units) so we will directly subtract them to find Zane`s weight. Or The limit of the luggage that each person can take in aero -plane is 20 kg. Ali`s luggage weighs 24000 g. How much weight is over the limit? Limit of Luggage = 20 kg = [20 x 1000] kg = 20000g. Ali`s luggage       =                                          24000 g Weight more than limit                = [24000-20000] g = 4000g. Now convert grams into kilograms, as; [4000 / 1000] = 4 kg. Repeat the whole process once again if they could not understand.
 Activity 3 Write the following expression on the board: as; Add 163 kg and 111 g to 21 kg and 690 g. Explain them that first we put kg in kg`s column and g in g`s column then added kilograms into kilograms and grams into grams. Ask the students to add or subtract the expressions involving similar units: as; i)                       75 kg,      888 g   +   170 kg,    501 g = ____________? ii)                      90 kg,      400 g   +     11 kg,    905 g = ____________? iii)                   178 kg,      388 g   –     59 kg,    430 g = ____________? iv)                     32 kg,      332 g   –     14 kg,    581 g = ____________?

Sum up / Conclusion

• Finish this lesson by asking different students to repeat the key concepts that we have learnt today, as;   1 kg = 1000 g
• Kilograms are used to measure heavy objects, whereas grams are used for lighter objects
• Similar units can be added or subtracted only, if units are not similar, we make them similar before addition or subtraction.
• We multiply kg by 1000 to convert kg to g and divide g by 1000 to get kg.
• If expressions involve mix units like kg & g both, we write kg below kg and g below the g and then we add or subtract.

Assessment

• Now assign different questions to the students to assess whether they have got your points or not.
• Take weight of your friend and his /her school bag and find difference which one is heavier, as;
• Ali`s weight is 25 kg and 320 g whereas his bag`s weight is 5 kg and 20 g. which one is heavier and how much?
• Subtract 25 kg, 320 g – 5 kg, 20 g = __________?