If n people walk into a bar the first asks for a pint of lag

If n people walk into a bar, the first asks for a pint of lager, the second asks for half a pint, the third for a quarter, etc... (Each person requesting half of what the former ordered). How many pints of lager will the bartender pour in total?

Solution

n poeple:

1st : 1 pint ; 2nd 1/2 pint ; 3rd person : 1/2(1/2)..... and so on

Total pints : 1 +1/2 + 1/4 + 1/8 .... 1/2^n-1

Sum = ( 1- 1/2^n)/(1 - 1/2) = 2( 1- 1/2^n) Total pints bartender pour in