Measuring and comparing lengths - Orchids The International School
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Measurements

Measuring and comparing lengths

Length is a measure of how long something is. We use rulers or tape to measure lengths.

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  • Most of the times, we measure the length in millimetres (mm), centimetres (cm), meters (m), and kilometres (km) as a unit of length. These are standard units of length.
  • In daily life, we use a centimetre scale to measure length.
  • The tailors in their shop use a metre scale to measure any cloth.

Measuring Length Using Ruler

  • The object to be measured should be kept properly on the scale such that one of its ends coincides with the zero (0) mark on the scale.
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  • The object to be measured should be kept parallel to the scale and touching the scale.
  • While taking the reading of the other end of the object, the mark of the scale and your eyes should all be in a straight line on the scale.
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  • Hence, the reading of the length from the ruler is 13 cm. The length of the pencil is 13 cm.
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Also, height can be measured using scales or tapes. We use centimetres (cm) and metre (m) as units to measure height. Always start measuring from the 0 mark to get an accurate reading.

Relation Between cm-mm, m-cm and km-m

The standard unit of length is ‘Metre’. Conversion from one unit to another unit is easy if we know the relationship between the units.

  • cm - mm: 1-centimetre length is equally divided into 10 small parts and each part is called a millimetre (mm).
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    So, 1 cm = 10 mm or 10 mm = 1 cm

  • m-cm: 1-metre length is equally divided into 100 small parts and each part is called a centimetre (cm). So, So, 1 m = 100 cm or 100 cm = 1 m
  • km-m: 1-kilometre length is equally divided into 1000 small parts and each part is called a metre (m). So, 1 km = 1000 m or 1000 m = 1 km

Conversion from cm to mm, m to cm, and km to m

  • To convert cm to mm, we multiply the length of the object by 10.
  • class="learn-green-text">Example: Convert from 24 cm to mm.

    Answer:24 cm = 24 × 10 = 240 mm

  • To convert m to cm, we multiply the length of the object by 100.
  • class="learn-green-text">Example:Convert from 30 m to cm.

    Answer:30 m = 30 × 100 = 3000 cm

  • To convert km to m, we multiply the length of the object by 1000.
  • class="learn-green-text">Example:Convert from 45 km to m.

    Answer:45 km = 45 × 1000 = 45000 m

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Real-Life Problems

  1. Sahil has to colour a 100 m bamboo. He is instructed to colour 20 m of the bamboo with red, 30 m with blue and 40m with orange. What length of the bamboo is left uncoloured?
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    Answer:

    Sahil coloured 20 m + 30 m + 40 m bamboo

    20 m + 30 m + 40 m = 50 m + 40 m = 90 m

    So, the uncoloured portion left is 100 m – 90 m = 10 m

    Hence, 10m of the bamboo is left uncoloured.

  3. Julie’s grandfather has a 3 m long ribbon. He decided to divide the length of the ribbon among his four grandsons and daughters. How much ribbon will each one get?
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    Answer:

    3 m = 3 × 100 cm = 300 cm

    Grandfather has 4 grandsons and daughters.

    So, each of them will get 300 cm ÷ 4 = 75 cm

    Hence, each one will get 75 cm ribbon.

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