7.2. There are 11 kg of cereal. How can you measure out 1 kg of cereal using two weighings on a balance scale, if you have one 3 kg weight?
Solution. First weighing: place a weight (3 kg) on one scale pan, and on the other, initially 11 kg of grain, and keep pouring grain onto the first pan until equilibrium is achieved. We get 3 kg (weight) + 4 kg (grain) $=7$ kg (grain) (since $3+x=11-x=>x=4$). Second weighing: from the obtained 4 kg of grain, pour out 3 kg of grain to balance the 3 kg weight. The weight of the remaining grain is 1 kg.