3.1. From a vessel filled to the brim with delicious 100% juice, fifth-grader Masha drank 1 liter of juice during the day, and in the evening, she added 1 liter of water to the vessel. The next day, after thorough mixing, she drank 1 liter of the mixture and in the evening added 1 liter of water. On the third day, after mixing the mixture again, she drank 1 liter of this mixture and in the evening added 1 liter of water. The next morning, her parents found out that the volume of water in the vessel was 1.5 liters more than the volume of the remaining juice. How many liters of juice did Masha drink in total? If the answer to the question is not unique, indicate the sum of all possible values of the desired quantity.
Answer: 1.75. Solution. Let the volume of the container in liters be x. After the first day, there will be $(x-1)$ liters of juice left, after the second day - $\frac{(x-1)^{2}}{x}$ liters of juice, and after the third day - $\frac{(x-1)^{3}}{x^{2}}$ liters of juice. According to the condition, we get the equation $x-\frac{(x-1)^{3}}{x^{2}}=\frac{(x-1)^{3}}{x^{2}}+1.5$ $\Leftrightarrow x^{3}-(x-1)^{3}=(x-1)^{3}+\frac{3}{2} x^{2} \Leftrightarrow 2 x^{3}-9 x^{2}+12 x-4=0 \Leftrightarrow(x-2)^{2}\left(x-\frac{1}{2}\right)=0$. According to the condition $x>1$, therefore $x=2$ (this is the volume of the container), the amount of juice left is $\frac{(2-1)^{3}}{2^{2}}=\frac{1}{4}$ liters. Thus, Masha drank $2-0.25=1.75$ liters.