Answer :
You can use the associative property because the order does not matter with 2 or more numbers if you are just finding the sum.
26 + 19 + 34 + 21 = 100 students total
The number of students in the four sixth-grade classes are 26, 19, 34 and 21. Use properties to find the total number of students in the four classes.
26, 19, 34, and 21.