Help with fraction riddle please?

A few years ago I took my students on field trips related to the projects we were working on. At one point, we went to several places in Seattle to gather research. I got some parents to help me, and we scheduled four field trips in one day. Four students went to the Burke Museum, five went to the EMP Museum, eight went to the science museum, and the five remaining students went to the Aquarium. The problem we ran into was the the school cafeteria staff had made seventeen submarine sandwhices for the kids for lunch. They gave three sandwhiches to the four kids going to the Burke museum, The five kids in the second group got 4 subs, the eight kids going to the science museum got seven subs, and that left three for the five kids going to the Aquaium. Now, we didn't eat together obviously, because if they were i would really like to work out a fair system- one where i would know how many subs to give each group when we go on field trips this year.