Answer:
commutative property of addition.
a sequence of additions can be done in any order and the total remains the same.
Explanation:
so, we can actually do
27 + 3 + 15 + 5
and now it is easy to combine 27+3 to 30 and 15+5 to 20, and to make the final calculation of 30 + 20 = 50 in our minds.