Question

18. You and your friend are selling your old CDs. Your friend sells 14 the first

Answer 1

9514 1404 393

Answer:

  = x + y + 20

Step-by-step explanation:

There are a couple of ways you could write this.

  friend sales + your sales

  = (14 +x) +(y +6)

  = (x +14) +(6 +y) . . . . commutative property used twice

  = x +14 +6 +y = x +20 +y

  = x + y + 20 . . . . . . . commutative property used again

__

  first-day sales + second-day sales

  = (14 +y) + (x +6)

  = (y +14) +(6 +x) . . . . commutative property used twice

  = y +14 +6 +x = y +20 +x

  = y +x +20 . . . . . . . . commutative property used again

  = x + y + 20 . . . . . . . and again

_____

Additional comment

We also used the associative property (to move parentheses) and the properties of addition of integers to simplify the sum. We have chosen to put the variables in lexicographical order, a sort of standard.