Math problem

Today i have learnt how to solve a problem using quarters for an ex sample- There were 12 pineapples each pineapple we need to cut 2 hole pineapples  into 2/3  to make a pineapple pie how many pineapples dose he need to make 18 pies? i put 18 pineapples out and made them into 2/3 i shade in 2 in each pineapple and there were 1 left in each pineapple i add the left overs and circled 2 pineapples of each and counted it up so i got 9 + 18 = 27 -6 = 18.