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An irrigation machine uses 1.5 litres of fuel for every three hours.
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How many litres will the machine use in five hours?
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We’re told in the question that, in three hours, the irrigation machine uses 1.5 litres of fuel.
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We’re asked to calculate the number of litres used in five hours.
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A sensible start point here would be to calculate how much fuel is used in one hour.
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To get from three hours to one hour, we divide by three.
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This means, to calculate the amount of fuel, we need to divide 1.5 litres by three.
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1.5 divided by three is equal to 0.5.
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We know this as 15 divided by three equals five.
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And using our knowledge of place value, 1.5 divided by three must therefore be equal to 0.5.
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As we now know the amount of fuel used in one hour, we can calculate the amount used in five hours by multiplying by five.
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We need to calculate 0.5 multiplied by five.
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Once again, we know that five multiplied by five is equal to 25.
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This means that 0.5 multiplied by five must be equal to 2.5.
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We can therefore conclude that if the irrigation machine uses 1.5 litres of fuel in three hours, it will use 2.5 litres in five hours.