Math Question....

Landshark44 · 10-03-2013, 08:29 PM

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 · 10-03-2013, 08:32 PM

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 · 10-03-2013, 08:34 PM

r = -2?

DaddyTorgo · 10-03-2013, 08:36 PM

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 · 10-03-2013, 08:41 PM

Quote:

Originally Posted by cuervo72

r = -2?

that's what i got too

cuervo72 · 10-03-2013, 08:42 PM

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 · 10-03-2013, 08:44 PM

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

mathway.com says r=-2

Shkspr · 10-03-2013, 08:44 PM

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

cuervo72 · 10-03-2013, 08:46 PM

The negative of my negative is my positive...

korme · 10-03-2013, 08:49 PM

Man, I don't miss that kind of math

Landshark44 · 10-03-2013, 08:51 PM

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 · 10-03-2013, 08:52 PM

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

ColtCrazy · 10-03-2013, 08:58 PM

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 · 10-03-2013, 09:07 PM

I get -2 as well.

panerd · 10-03-2013, 09:15 PM

Quote:

Originally Posted by 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....

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 · 10-03-2013, 09:15 PM

Thanks, guys...

ColtCrazy · 10-03-2013, 09:19 PM

Quote:

Originally Posted by panerd

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 · 10-03-2013, 09:23 PM

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

britrock88 · 10-03-2013, 09:27 PM

Quote:

Originally Posted by DaddyTorgo

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 · 10-03-2013, 09:49 PM

Quote:

Originally Posted by sovereignstar v2

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.

DaddyTorgo · 10-03-2013, 09:49 PM

Quote:

Originally Posted by britrock88

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 · 10-03-2013, 10:46 PM

Someone needs a new math teacher.

EagleFan · 10-03-2013, 10:53 PM

How on earth does the teacher get -27?

EagleFan · 10-03-2013, 10:59 PM

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 · 10-03-2013, 11:12 PM

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 · 10-03-2013, 11:14 PM

Quote:

Originally Posted by 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...

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

OldGiants · 10-04-2013, 07:27 AM

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

Desnudo · 10-04-2013, 07:46 AM

Quote:

Originally Posted by EagleFan

How on earth does the teacher get -27?

Probably an error in the teacher's book.

ntndeacon · 10-04-2013, 07:54 AM

Quote:

Originally Posted by 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)

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 · 10-04-2013, 08:48 AM

Quote:

Originally Posted by 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.

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!

Matthean · 10-04-2013, 09:22 AM

Quote:

Originally Posted by Desnudo

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 · 10-04-2013, 09:27 AM

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 · 10-04-2013, 10:24 AM

The wonders of the internet answer all questions!

Chief Rum · 10-04-2013, 10:28 AM

Quote:

Originally Posted by ColtCrazy

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 · 10-04-2013, 10:41 AM

Astounding.

ColtCrazy · 10-04-2013, 09:47 PM

Quote:

Originally Posted by Chief Rum

Ping: Quiksand

Bad pronouns. Yes, I know.

EagleFan · 10-04-2013, 10:41 PM

Quote:

Originally Posted by Chief Rum

Ping: Quiksand

Quote:

Originally Posted by QuikSand

Astounding.

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

10-03-2013, 08:34 PM	#3
cuervo72 Head Coach Join Date: Dec 2002 Location: Maryland	r = -2? __________________ null

10-03-2013, 08:36 PM	#4
DaddyTorgo Hall Of Famer Join Date: Oct 2002 Location: Massachusetts	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? Last edited by DaddyTorgo : 10-03-2013 at 08:39 PM.

10-03-2013, 08:42 PM	#6
cuervo72 Head Coach Join Date: Dec 2002 Location: Maryland	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 __________________ null

10-03-2013, 08:46 PM	#9
cuervo72 Head Coach Join Date: Dec 2002 Location: Maryland	The negative of my negative is my positive... __________________ null

10-03-2013, 08:52 PM	#12
DaddyTorgo Hall Of Famer Join Date: Oct 2002 Location: Massachusetts	mathway.com says the teacher is wrong - unless i typed it in wrong... __________________ If I've ever helped you and you'd like to buy me a coffee, or just to say thanks, I have my Bitcoin and Ethereum addressed listed below :) BTC: bc1qykhsfyn9vw4ntqfgr0svj4n9tjdgufryh2pxn5 ETH: 0x2AcdC5cd88EA537063553F5b240073bE067BaCa9

10-03-2013, 08:32 PM	#2
DaddyTorgo Hall Of Famer Join Date: Oct 2002 Location: Massachusetts	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?

10-03-2013, 08:44 PM	#7
DaddyTorgo Hall Of Famer Join Date: Oct 2002 Location: Massachusetts	gah - I messed up somewhere obviously. LOL. It's been a while. mathway.com says r=-2

10-03-2013, 08:44 PM	#8
Shkspr College Benchwarmer Join Date: Nov 2000 Location: Amarillo, TX	I assume the point of the exercise is to keep track of the change in signs as expressions nest.

10-03-2013, 08:49 PM	#10
korme Go Reds Join Date: May 2001 Location: Bloodbuzz Ohio	Man, I don't miss that kind of math

10-03-2013, 08:51 PM	#11
Landshark44 High School Varsity Join Date: Feb 2006 Location: Atlantic City, NJ	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....

10-03-2013, 08:58 PM	#13
ColtCrazy College Starter Join Date: Oct 2000 Location: Midwest	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. __________________ The Field Generals and Statis Pro Basketball Super League

10-03-2013, 09:07 PM	#14
Eaglesfan27 Hall Of Famer Join Date: Nov 2002 Location: New Jersey	I get -2 as well. __________________ Retired GM of the eNFL 2007 Super Bowl Champion Philadelphia Eagles (19-0 record.) GM of the WOOF 2006 Doggie Bowl Champion Atlantic City Gamblers. GM of the IHOF 2019 and 2022 IHOF Bowl Champion Asheville Axemen.

10-03-2013, 09:15 PM	#16
Landshark44 High School Varsity Join Date: Feb 2006 Location: Atlantic City, NJ	Thanks, guys...

10-03-2013, 09:23 PM	#18
sovereignstar v2 hates iowa Join Date: Oct 2010	I like that DT used the word 'easy' twice and came up with an answer that no one else did.

10-03-2013, 10:46 PM	#22
thealmighty Pro Starter Join Date: May 2003 Location: heaven	Someone needs a new math teacher. __________________ Check out The Unofficial FOFC Movie Guide Here

10-03-2013, 10:53 PM	#23
EagleFan Hall Of Famer Join Date: Nov 2000 Location: Mays Landing, NJ USA	How on earth does the teacher get -27? __________________ The EagleFan YouTube Channel - Reactions Soarin' & Scratchin' YouTube Channel - We react to music, videos, TV, we talk, we are planning some field trips Soarin' & Soothin' - Meditation, Relaxation, and Sleep Aid; mental health is important

10-03-2013, 10:59 PM	#24
EagleFan Hall Of Famer Join Date: Nov 2000 Location: Mays Landing, NJ USA	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... __________________ The EagleFan YouTube Channel - Reactions Soarin' & Scratchin' YouTube Channel - We react to music, videos, TV, we talk, we are planning some field trips Soarin' & Soothin' - Meditation, Relaxation, and Sleep Aid; mental health is important

10-03-2013, 11:12 PM	#25
fantom1979 College Benchwarmer Join Date: Apr 2008 Location: Sterling Heights, Mi	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.

10-04-2013, 07:27 AM	#27
OldGiants College Benchwarmer Join Date: Oct 2000 Location: Location, Location, Location	Woolram Alpha gave me -2 in less than ten seconds. __________________ "The case of Great Britain is the most astonishing in this matter of inequality of rights in world soccer championships. The way they explained it to me as a child, God is one but He's three: Father, Son and Holy Ghost. I could never understand it. And I still don't understand why Great Britain is one but she's four....while [others] continue to be no more than one despite the diverse nationalities that make them up." Eduardo Galeano, SOCCER IN SUN AND SHADOW

10-04-2013, 09:27 AM	#32
Ronnie Dobbs3 High School Varsity Join Date: Feb 2013	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.

10-04-2013, 10:24 AM	#33
DanGarion Coordinator Join Date: Nov 2003 Location: The Great Northwest	The wonders of the internet answer all questions! __________________ Los Angeles Dodgers Check out the FOFC Groups on Facebook! and Reddit! DON'T REPORT ME BRO!

10-04-2013, 10:41 AM	#35
QuikSand lolzcat Join Date: Oct 2000 Location: Annapolis, Md	Astounding.

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