3.2 Length

• Units of length: centimetre (cm), decimetre (dm), metre (m), decametre (Dm), hectometre (Hm)
• Conversion tables for cm, dm, m, Dm and Hm
• Operations involving units of length
• Perimeter of plane figures, including combined shapes
• Circumference of circles and the relationship circumference to diameter (Pi)

• convert units of length from one form to another involving cm, dm, m, Dm, Hm in learning situations
• perform operations involving units of length in different situations
• work out the perimeter of plane figures in different situations
• work out the circumference of circles in different situations
• promote the use of length in real-life situations

“Why do we use different units of measuring length?”

“How do we measure the perimeter of different objects?”

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1. Units of length
   40 min · 1 practice tasks · quiz
   Name cm, dm, m, Dm and Hm, and say why Kenya uses different units for a finger, a desk, a classroom and a 100 m track.
2. Converting units of length
   40 min · 1 practice tasks · quiz
   Convert among cm, dm, m, Dm and Hm by multiplying or dividing by 10 for each step on the ladder.
3. Operations with lengths
   40 min · 1 practice tasks · quiz
   Add, subtract, multiply and divide lengths after converting every measurement to the same unit.
4. Perimeter of plane figures
   40 min · 1 practice tasks · quiz
   Find the distance around squares, rectangles, triangles and combined shapes by adding the outer sides.
5. Circumference and Pi
   40 min · 1 practice tasks · quiz
   Measure circular objects to find that circumference divided by diameter is about 22/7, and name that number Pi.
6. Using circumference and length
   40 min · 1 practice tasks · quiz
   Apply C = πd and C = 2πr to a bicycle wheel, a flower bed and a track, and choose sensible units for real jobs.