Alternating series/Leibniz criterion/Coffee in student flat/Exercise

In a shared flat for students, Student 1 prepares coffee and he puts the amount ${}x_{1}$ of coffee in the coffee filter. Then Student 2 looks horrified and says: "Do you want us all to be already completely awake“? and he takes the amount of coffee ${}x_{2}<x_{1}$ back out of the filter. Then Student 3 comes and says: "Am I in a flat of sissies“? and he puts back an amount of coffee ${}x_{3}<x_{2}$

in it. So it goes on indefinitely, alternating between putting in and taking out smaller amounts of coffee from the coffee filter. How can one characterize if the amount of coffee in the filter converges?

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