If we group the terms differently, it doesn't matter.
This is called the associative property of addition. As long as you still have all of the terms, and there are no other operations (subtraction, multiplication, etc.), the final answer will remain the same no matter how the terms are grouped.
The fifth graders were given sandwiches for lunch during their field trip. Nathan ate 5/6 of his sandwich, Leroy ate 7/8 of his sandwich, and Sofia ate 5/8 of her sandwich. Who ate the greatest amount of their sandwich? ... Nathan ate 20/24, Leroy ate 21/24, and Sofia ate 15/24 meaning Leroy ate the most.