Ice cream  logic puzzle
At a particular ice cream van two types of ice creams are being sold. The small one costs 1 dollar, the big one 2 dollars. Marsha puts an amount of 2 dollars one the counter and gets without asking the big ice cream. Martha also would like to have an ice cream. She also puts an amount of 2 dollars on the counter. Then the ice cream seller asks her which ice cream she would like to have. Assuming that the persons do not know each other, how can you explain their behavior. 
Explanation
Marsha puts two 1 dollar notes on the counter, so that the seller immediately knows which ice cream she would like to have.
Martha however puts down a 2 dollar note.
