Lesson Planning of Addition and Subtraction of Units of Lengths
Subject Mathematics
Grade 4^{th}
Students` Learning Outcomes
 Add and subtract expressions involving similar units of lengths.
 Use appropriate units to measure lengths of different objects.
 Solve real life problems involving conversions, addition and subtraction of units of lengths.
 Information for Teachers
 Milometer, meter, centimeter and millimetre are units of measurement written as km, m, cm and mm respectively.
 Conversion of units can be done by using the following rules, as;
1 KM = 1000 M
1 M = 10 CM
1 CM = 10 MM
 With the help of these units of length we can find required measurements and can also change them into appropriate measure.
 We multiply while converting greater to smaller unit and use division while converting small unit to greater.
 During this lesson consult text book at each lever wherein it is required
Material / Resources
Writing board, chalk/marker, scale, measuring tape, textbook
Introduction
 Write on the board kilometres, meters, centimetres and millimetres.
 Ask the students which unit can be used for measuring the following: as;
 Distance between cities (Milometers)
 Length of a pencil (Centimetre)
 The thickness of finger nails (Millimetres)
 Tell them that we have learnt basic units of length in previous lectures.
 Today we will learn how to add and subtract these units.
 Ask them can we add millimetre into kilometre? (Expected answer would be as; No)
 In fact, only similar units can be added or subtracted
 We make different units similar before adding and subtracting.
Development
Activity 1

Activity 2

Sum up / Conclusion
 Same units can be added or subtracted only.
 If we want to add them we first convert them in same units.
 The smallest unit for measuring length is millimetre.
 The greatest unit for measuring length, height or distance is kilometers.
 We multiply while converting greater to smaller unit and use division when we convert smaller to greater unit.
Assessment
 Give following problems to the students to assess them: as;
 Distance between cities A to B is 450 kilometres. If the driver has covered 291 kilometres, then how many kilometres are left to be covered?
 Choose the appropriate units for measuring the following lengths: as;
 Length of shoes:
(a (a) Meter (b) centimetres (c) millimetres
 Width of an eraser:
(a (a) Millimetre (b) meters (c) kilometres
 Assign following questions to the students: as;
Follow up
 Choose the best estimate to answer each question: as;
 About how tall is a plastic water bottle?
(a) 20 cm (b) 20 km
© 20 m (d) 20 mm
 About how long a pens nib is?
(a (a) 2 cm (b) 2 mm
(c) 2 m (d) 2 km
 About how away from can be my school from my home?
(a (a) 1 m (b) 1 km
© 1 cm (d) mm