Reasoning and solution:/
The 3 elements:
The amount in each group: 2/9 of a cake
The number of groups: 3
The total amount in all the groups: the amount of the cake by 3 people?
We multiply the amount in each group, 2/9 of the cake, with the number of groups, 3, to find the total amount of cake in all 3 groups, the total amount of cake all 3 people had:
3 x 2/9 of the cake =6/9 of the cake =2/3 of the cake
They three had 2/3 of the cake altogether.