Math Question....

[Landshark44]

My two sons, and the teacher all have different answer to this question....

Any help solving would be appreciated...

3(r+1)-[2(3-2r)-3(3-r)]=2(r+5-4)

[DaddyTorgo]

I look at something like this and all that comes to mind is the old "work from the inside out" maxim.

Should be fairly straightforward with that, right?

[cuervo72]

r = -2?

[DaddyTorgo]

3(r+1)-[2(3-2r)-3(3-r)]=2(r+5-4)

right side is easy, it's 2r+2

left side is trickier, but you work from the inside out, so

3(3-r) is 9-3r

2(3-2r) is 6-4r

3r+3-6-4r-9-3r=2r+2

when you expand it all out, right? from there it should be easy.

-2r=-14

r=7?

[lighthousekeeper]

r = -2?

that's what i got too

[cuervo72]

Ok, here's my work.

3r + 3 - [6 - 4r - 9 + 3r] = 2r + 2

3r + 3 - [ -3 - r ] = 2r + 2

3r + 3 + 3 + r = 2r + 2

4r + 6 = 2r + 2

2r = -4

r = -2

[DaddyTorgo]

gah - I messed up somewhere obviously. LOL. It's been a while.

mathway.com says r=-2

[Shkspr]

I assume the point of the exercise is to keep track of the change in signs as expressions nest.

[cuervo72]

The negative of my negative is my positive...

[korme]

Man, I don't miss that kind of math

[Landshark44]

my 12 yr old got (-4)....
my 16 yr old got (-2)....

teacher says answer is (-27)

I don't have a clue, so I figure I'd ask you guys....

[DaddyTorgo]

mathway.com says the teacher is wrong - unless i typed it in wrong...

[ColtCrazy]

I'm getting r = -2 as well. The trick is remembering the negative/negative rule when you are working out the bracket and then eliminating the bracket later.

[Eaglesfan27]

I get -2 as well.

[panerd]

my 12 yr old got (-4)....
my 16 yr old got (-2)....

teacher says answer is (-27)

I don't have a clue, so I figure I'd ask you guys....

I always have two questions in situations like this... What is the point of assigning this problem in the first place and even if you think there is a point why assign it when you can't find the correct answer? I think the 16 year old is correct and I will assume it is the 12 year olds teacher.

[Landshark44]

Thanks, guys...

[ColtCrazy]

I always have two questions in situations like this... What is the point of assigning this problem in the first place and even if you think there is a point why assign it when you can't find the correct answer? I think the 16 year old is correct and I will assume it is the 12 year olds teacher.

Find it interesting as well that none of us got what the teacher got.

[sovereignstar v2]

I like that DT used the word 'easy' twice and came up with an answer that no one else did.

[britrock88]

gah - I messed up somewhere obviously. LOL. It's been a while.

mathway.com says r=-2

You forgot to carry the minus to the rightmost term of the left side of the equation when you expanded it.

[DaddyTorgo]

I like that DT used the word 'easy' twice and came up with an answer that no one else did.

LOL - hey I never said math was my subject or I'd get it right. :lol:

[DaddyTorgo]

You forgot to carry the minus to the rightmost term of the left side of the equation when you expanded it.

Ohhhh yeah. Whoops.

[thealmighty]

Someone needs a new math teacher.

[EagleFan]

How on earth does the teacher get -27?

[EagleFan]

Putting -27 in that makes it:

-81 + 3 - [(6+108)-(9+81)]=9(-27 + 5 -4)
-78 - [114-90]=9(-26)
-78 - 24 = -234
-102 = -234

Does not compute...

[fantom1979]

It is now a quest of mine to figure out how you can screw up the OOO to make this equal -27. I have not been successful so far.

[fantom1979]

Putting -27 in that makes it:

-81 + 3 - [(6+108)-(9+81)]=9(-27 + 5 -4)
-78 - [114-90]=9(-26)
-78 - 24 = -234
-102 = -234

Does not compute...

Bingo, very easy to disprove these equations in reverse. Teacher should realize that she is wrong pretty quickly.

[OldGiants]

Woolram Alpha gave me -2 in less than ten seconds.

[Desnudo]

How on earth does the teacher get -27?

Probably an error in the teacher's book.

[ntndeacon]

My two sons, and the teacher all have different answer to this question....

Any help solving would be appreciated...

3(r+1)-[2(3-2r)-3(3-r)]=2(r+5-4)

3(r+1)-[6-4r-9+3r]=2(r+1)
3(r+1)-[-r-3]=2r+2
3r+3+r+3=2r+2
4r+6=2r+2
2r=-4
r=-2

[ColtCrazy]

It is now a quest of mine to figure out how you can screw up the OOO to make this equal -27. I have not been successful so far.

Ha. I'm trying the same thing. Even if you completely flip everything in the bracket by accident, I get r= 2/3. I've tried several combinations of errors and the answer with the highest absolute value I'm getting is -14. The teacher must have a bad answer in their teacher's book. As a teacher, I'm hoping it's that (which, sadly, happens a lot in my books) because the alternative is that the teacher really screwed that problem up! :D

[Matthean]

Probably an error in the teacher's book.

I looked up a Calc. problem in a solutions manual, and it literally gave a full solution to a completely different problem.

[Ronnie Dobbs3]

To see if I could find the -27 online anywhere I googled it, and was heartened to see three different answers come up, none of which were right.

It's like the general stupidity of the world negates the internet when it comes to solving these things.

[DanGarion]

The wonders of the internet answer all questions!

http://i.imgur.com/YitPbNr.jpg

[Chief Rum]

Ha. I'm trying the same thing. Even if you completely flip everything in the bracket by accident, I get r= 2/3.

Ping: Quiksand

[QuikSand]

Astounding.

[ColtCrazy]

Ping: Quiksand

Bad pronouns. Yes, I know.

[EagleFan]

Ping: Quiksand

Astounding.

Holy crap, he's like Beetlejuice....