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Topic 5 of 8 · Grade 7

Measures: length, mass, capacity and time

60 seconds = 1 minute; 60 minutes = 1 hour; 24 hours = 1 day; 7 days = 1 week; 12 months = 1 year; 365 days (366 in a leap year).

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Units and conversions

  • Length: 10 mm = 1 cm; 100 cm = 1 m; 1 000 m = 1 km.
  • Mass: 1 000 g = 1 kg; 1 000 kg = 1 tonne.
  • Capacity: 1 000 ml = 1 litre.

Worked example: Change 3.45 km to metres.

3.45 × 1 000 = 3 450 m

Time

60 seconds = 1 minute; 60 minutes = 1 hour; 24 hours = 1 day; 7 days = 1 week; 12 months = 1 year; 365 days (366 in a leap year).

  • The 24-hour clock: 3:30 p.m. = 15:30.

Worked example: A bus leaves Bulawayo at 07:45 and arrives in Harare at 13:15. How long is the journey?

07:45 to 13:45 is 6 hours; subtract 30 minutes → 5 hours 30 minutes

Speed

Speed = distance ÷ time.

Worked example: A car travels 240 km in 3 hours. Find its speed.

240 ÷ 3 = 80 km/h

Temperature

Measured in degrees Celsius (°C). Water freezes at 0 °C and boils at 100 °C.

Exam tip: When converting to a smaller unit, multiply; to a larger unit, divide.

Check yourself

  1. How many grams are in 2.5 kg?
  2. Write 9:20 p.m. in 24-hour time.
  3. How many ml are in 1.75 litres?
Show answers
  1. 2 500 g
  2. 21:20
  3. 1 750 ml
Next topicShapes, area and volume

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