Answer:
1/12
Explanation:
It is given that :
Amount of cereal left = 1/3 of a box
Number of people amongst whom the box of cereal is to be divided equally = 4
Therefore, an equation representing this problem is :

where x = is the amount of the share each brother gets.
Therefore solving the equation, we get :



So, each brother got 1/12th of the cereal left.