3.2. A chocolate bar weighed 400 g and cost 150 rubles. Recently, to save money, the manufacturer reduced the weight of the bar to 300 g, and increased its price to 180 rubles. By what percentage did the manufacturer's revenue increase?
# Answer: 60

Solution. We will calculate by what percentage the cost of 1 kg 200 g has increased. Before the increase, this amount cost 450 rubles, and after the increase, it costs $180 \cdot 4=720$ rubles. The increase is 270 rubles on 1.2 kg, which originally cost 450 rubles. This is $\frac{270}{450} \cdot 100 \%=$ $60 \%$