Addition and Subtraction of Units of Mass / weight

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

Subject Mathematics

Grade 4th

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 = __________?

Follow up

  • Fill in the following table with the help of family members and write amounts of items given below used in a month and then add all the quantities: as ;

 

 

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