Given:
5)
total number of marbles =18
loses =6
a) To determine the fraction of the marbles that he loses, we divide the total number of loses by the total number of marbles:

b) To determine the fraction of marbles left, we divide the number of remaining marbles by the total number of marbles:

Therefore, he loses 6/18 or 1/3 of the total number of marbles while 12/18 or 2/3 left.