Solve Math Puzzle

Patrick walks into a bar in Dublin, orders three pints of Guinness and sits in the corner of the room, drinking a sip out of each pint in turn. When he had finished all three, he went back to the bar and ordered three more.

The barman says, “You know a pint goes flat soon after I pull it . Your pints would taste better if you bought one at a time.”

Patrick replies, “Well now, I have two brodders, one is in America and de odder in Australia and here I am in Dublin . When we all left home, we promised dat we’d drink dis way to remember de days we all drank togedder.”

The barman admits that this is a nice custom and says no more.

Patrick becomes a regular customer and always drinks the same way … ordering three pints and drinking a sip out of each in turn, until they are finished. One day, he comes in and orders just two pints. All the other regulars in the bar notice and fall silent. When he goes back to the bar for the second round, the barman says, "I don’t want to intrude on your grief but I wanted to offer my condolences on your great loss." Patrick looks confused for a moment, then the penny drops and he starts to laugh, “Oh no,” he says,

Bejesus, everyone is fine! Tis me … I’ve quit drinking!”