An irrigation machine consumes 4 liters of fuel in 2 working hours. If the machine works for 5 hours, how many liters will it consume?
The fuel is consumed at a rate of 4 litres per 2 hours, or litre/hour.
Write a relation. Let represent the number of hours the machine works, and represent the number of litres consumed in that amount of time.
Substitute 5 hours into the relation, and solve for .
So, the machine will consume 10 litres of fuel in 5 hours.