There are twelve children in the class who collected butterflies for the class project. The teacher added 40 butterflies that he collected, and between the teacher and the twelve students in all they collected 100. How many butterflies did each child collect?

Poorly phrased question. There is no way to determine how many butterflies EACH CHILD collected. The only thing that can be determined is how many butterflies the group of 12 children caught.

100 butterflies were collected, but the teacher added 40. Therefore, the group of children collected 60 (100-40) butterflies.

N=average # butterflies caught/child

N= 60 butterflies/12 children = 5 butterflies/child (on avg)