# Writing related subtraction sentences.

• Oct 17th 2010, 07:30 PM
ArchitecturalEngineer
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
• Oct 17th 2010, 07:38 PM
spruancejr
It appears to be correct since you're supposed to only use the sentence components given to you.
• Oct 17th 2010, 08:15 PM
ArchitecturalEngineer
now it says on a question " is subtraction commutative ( is there a commutative law of subtraction ) ? why or why not ?
• Oct 17th 2010, 09:37 PM
spruancejr
Commutativity is determined by asking if \$\displaystyle x-y=h\$ does \$\displaystyle y-x=h\$ also?

Think about it: 2-3 ≠ 3-2
• Oct 17th 2010, 10:00 PM
ArchitecturalEngineer
Quote:

Originally Posted by spruancejr
Commutativity is determined by asking if \$\displaystyle x-y=h\$ does \$\displaystyle 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
• Oct 17th 2010, 10:29 PM
spruancejr
Your problem states "describe the ONE situation in which subtraction is commutative". There is indeed a single case where subtraction is commutative.
• Oct 17th 2010, 10:30 PM
ArchitecturalEngineer
with zeros right ?
• Oct 18th 2010, 12:31 PM
spruancejr
Yes