As many as 50% of the respondents say that the first one is filled with cup number 4. If you gave us such a reply, we have a sad message for you: unfortunately, this is not the correct answer ….
In fact, the first cup to be filled will be number 5. Why? We explain this below.
Although logic indicates that cup number 4 should be filled first because the pipes leading to it are the lowest placed, it will not actually happen because they are … blocked!
Look closely at the drawing, leaving your calculations for a while, and then you will see that the coffee only reaches cup No. 5. Only this cup has the chance to be filled up, because all the other connections to the cups are blocked.