Leire invited ten friends to a birthday party. Once they have finished the lunch, she proposed a problem:
“If any of you guess how many chocolates are in the box without opening it, you would have it for you. To try to guess it I’ll give you some clues:
How many chocolates are there in the box?
Some of the participants of one parede can be three by three, five by five or twenty-five by twenty five; but they can’t be placed no way four by four or nine by nine.
How many participants are there if we know that there are between 1000 and 1250 people?