# Math Help - Writing related subtraction sentences.

1. ## Writing related subtraction sentences.

ok i'm in the book prealgebra 5th edition bittinger * ellenbogen *johnson and i had to write a related addition sentences such as for 20 - 8 = 12 it would be 12+8=20 but after those problems it has " write two related subtraction sentences " and they have some of the answers in the back of the book so i know this is right for 6 + 9 = 15 its 6 =15-9 ; 9=15-6 but then i came into 8 + 0 = 8 and what i have is 8 - 0 = 8 ; 0 = 8 - 8 and i don't know if its rite or not cause the answer is not in the back of the book

2. It appears to be correct since you're supposed to only use the sentence components given to you.

3. now it says on a question " is subtraction commutative ( is there a commutative law of subtraction ) ? why or why not ?

4. Commutativity is determined by asking if $x-y=h$ does $y-x=h$ also?

Think about it: 2-3 ≠ 3-2

5. Originally Posted by spruancejr
Commutativity is determined by asking if $x-y=h$ does $y-x=h$ also?

Think about it: 2-3 ≠ 3-2
well if your saying its not i think it has to be because 4 questions lator it asked " describe the one situation in witch subtraction is communutative "

i still don't have the answers for ither

6. Your problem states "describe the ONE situation in which subtraction is commutative". There is indeed a single case where subtraction is commutative.

7. with zeros right ?

8. Yes