The scene
Science Society · Experiment tableA reserved bottle of ink turns up inside an experiment box. Three participants had prepared containers with different amounts of liquid. The ink was added to one of their containers.
An assistant measured its contents after two experimental steps. The procedure was recorded, but the container’s label came off. Reversing the steps reveals the original amount.
What we know for certain
One of these people used the ink in their own container. The stated starting amount already includes that ink. There was no evaporation, spillage or other transfer. Each step happened exactly once, in the stated order, and the measurements are exact.
The three accounts
Isona Prat
Student«My container started with twenty millilitres.»
Joan Serra
Activity leader«Mine contained thirty.»
Kenia Sol
Assistant«I prepared forty millilitres.»
Examine the evidence
0 of 5 openedOpening these five clues does not cost points.
01The first step
The assistant removed exactly half the liquid from the chosen container and kept it separately. None was put back later.
02The second step
The assistant then added ten millilitres of clean water to the liquid remaining in the container.
03The final reading
The container finished with twenty-five millilitres. The volume marking was read correctly.
04The starting amounts
The records confirm Isona: 20; Joan: 30; Kenia: 40 millilitres. Each person had only their own container.
05The located ink
Analysis confirms that the tested container held all the reserved ink at the start. None was in the other two containers.