Grandpa Mick opened a pint of ice cream. He gave his youngest grandchild 1/5 of the ice cream and his middle grand child 1/4 of the remaining ice cream. Then, the oldest grandchild 1/3 of the ice cream that was left after serving the others.

13/60 was left of the ice cream.

Step-by-step explanation:

4/5 was left after the first, which can also be written as 16/20. 16/20 - 1/4 (also written as 5/20), which leaves 11/20 which can also be written as 33/60. 33/60 - 1/3 (also written as 20/60) which leaves 13/60 left.