What is the minimum number of times one needs to measure to get 298 litres of water from a tank, if the measuring cylinders have capacities 1 litre, 6 litres, 25 litres and 100 litres?<br/>

In 4 measurements, to get close to 298, we would need three 100-litre measurements and one correction. But 300-1=299, 300-6=294, 300-25=275; none gives 298. So 4 is impossible.
In 5 measurements, it is possible: measure 100 L three times and then remove 1 L twice.
Net water = 100+100+100-1-1 = 298 L.
So the minimum number of measurements is 5.