

Conversions  Estimation
 In order to be able to make and manipulate a range of measurements we need to be able to convert measurements into units which suit our situation. We can measure an object using quite small units. This permits the measure to be more accurate. If we want to, we can convert our measurement into a more manageable unit when we have finished our calculations. The following diagram shows how we can convert length measurements into smaller or larger units. For example, to convert a measurement in metres to centimetres, multiply the number of metres by 100. To convert a measurement in centimetres to metres, divide the number of centimetres by 100. Example
1: Full explanation of length measurement conversion.
Some other measurement conversion examples are shown below. Example
2: Full explanation of volume measurement conversion. Example
3: Full explanation of area measurement conversion.
Although builders would measure the length of a swimming pool or the height of a wall in millimetres, we would probably use metres. Example
4: Measurement conversion.
We use measurement regularly in our daily lives. Often, an estimate may be sufficient, but in other cases accurate measurement is very important. Engineers and builders need to be as exact as possible in their measurements when constructing buildings. Scientists need to be extremely accurate when mixing minute amounts of chemicals. Depending
on our situation, we make choices about how we make measurements.
We might consider the following things:  an estimation using informal units may be sufficient for our needs  having an idea of benchmarks helps us to make estimations. Informal
or Nonstandard units Example
5: Measuring with informal units.
Indicating accuracy of measurements Is a measurement of 2km the same as a measurement of 2.000 km? Certainly the decimal number 2 has exactly the same value as the number 2.000. With measurement, however, these two measures have a different meaning. The number of places indicates the accuracy of the measurement. If a distance is given as 2 km, this means that it is closer to 2 km than to 1 km or 3 km. It is somewhere between 1.5 and 2.5 km. The measurement of 2.000 km indicates a much more precise measurement. It is nearer to 2.001 km than to 1.999 km. Writing the measurement as 2.000 km indicates that the distance has been measured to the nearest metre. If the distance was given as 2.0000 km, it would indicate that it has been measured to the nearest one tenth of a metre. A temperature given as 23.6 degrees indicates that it has been measured to the nearest tenth of a degree. If the temperature is given as 23.60 degrees, this indicates it has been measured more accurately (to the nearest one hundredth of a degree). If it is given as 23 degrees, it has been measured less accurately. Be sure to consider carefully the number of decimal places you use when reporting a measurement. These significant figures are very important in scientific and engineering work.
5. Joshua estimates that the length of his desk is about 15.5 times the width of his palm. He measures his palm and finds it is 9 cm wide. What is the approximate length of his desk? 6. Naomi measures a bookcase and finds it is 160.5cm high. Matthew measures the same bookcase and finds it is 160.50cm high. Comment on their measurements. 7. Complete the following statements. (a) 385 centimetres = ____________ metres (b) 9.35 kilograms = _____________ grams (c) 49 millilitres = _______________ litres (d) 0.054km = __________________ centimetres (e) 8647km = ___________________ metres 8. I have 3m 65cm of alfoil left on my roll. How many centimetres are left? 9. Martin’s stride is 80 cm. How many metres does he walk if he takes 60 strides? 10. How many 25g packets of rice can be made from 1 kg? 11. How many seconds are there from 9.00pm Sunday to 7.00am the next day,Monday? 12. Which is larger 3250 ml or 0.325 litres? Give a reason for your answer.


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