To Add: (300 + 586) + 114
We know that by associative property, (a+b)+c = a+(b+c).
So, (300+586)+114=300+(586+114)
Let us check both sides,
(300 + 586) + 114 = 886 + 114 = 1000
300 + (586 + 114) = 300 + 700 = 1000
We can see both the sides give the same result. So the associative property is proved.