Answer the following questions:

a) Is the following equality true? What property is used?

$$15+(96+4)=(15+96)+4$$

b) Is the following equality true? What property or properties is/are used?

$$(1+6)+9=1+(9+6)$$

### Development:

a) On both sides of the equality, the addends are the same, but the additions are done in a different order. The associative property tells us that the result is the same in both cases.

b) On the left side of the equality, the first sum that we do is $$1+6$$ and then we add $$9$$. On the right side, we first add $$9+6$$, which is the same as $$6+9$$ (using the commutative property), and then $$1$$ is added. Using the associative property, we know that the result is the same.

### Solution:

a) The equality is true, and the property used is the associative property.

b) The equality is also true. Here the commutative and the associative properties are used.