Question 100946
Hello!
I usually justify these kind of problems by stating the property used to each steps.


=5n+(20+9n)  APA  (we used the associative property of addition to get this)
=5n+(9n+20)  CPA (we used the commutative property of addition to get this)
=(5n+9n)+20  APA  (we used the associative property of addition to get this)
=(5+9)n+20   DPMA(we used the distributive property of multiplication to get this)
=14n+20      ADDITION(we just simply add to get this)



*associative property of addition means that if you change the groupings of the numbers,it won't affect the sum.
*commutative property of addition means that if you change the order of the numbers it won't affect the sum.