cho hỏi câu này với ạ:
there are 5 blues, 4 orange ball and 2 yellow balls in a bag. S will be blindfolded before she take the balls out, one at a time
how many balls must S take out in order to get 4 balls of the same colour?
( note that has to begin with 1 bule, 1 orange and 1 yellow ball )
cảm ơn các men