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
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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
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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.
