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