I have encountered a voting problem:

Assuming a situation where 18 students divided into 4 groups, each group propose a project idea and they are going to vote for their favourite project among the 4 ideas proposed. The one with the most votes will be the winner project idea. If each group have a different number of students and they could vote for their own project if they like it, is there any mathematical or statistical methods that could eliminate the error or weigh each vote according to the group size to make the voting fairer?