the total grapes is a whole, that is 100% or simply put 1, all the fractions must add to 1 to get the total. So we have:
akeem: 1/2
jamila: 1/3
kim: x
1/2 + 1/3 + x = 1
3/6 + 2/6 + x = 1
5/6 + x = 1
x = 1 - 5/6
x = 6/6 - 5/6
x = 1/6
so kim has 1/6 still