Help me maths.

"Frank Grimes" (FrankGrimes)
03/01/2016 at 19:55 • Filed to: None

this was on a math test and I figured out the answer but not how to form a algebraic expression to solve it.

A farmer has chickens and pigs that total 28. There are a total of 72 Legs.
How many pigs does he have?

Use an algebraic expression to find the answer.

I could not for the life of me figure out any sort of expression for this and I took the test last thursday and it still bugs me. I blame my teacher throwing us a curve ball.

DISCUSSION (66)

djmt1 > Frank Grimes
03/01/2016 at 20:01

Wait, math or maths? I can only help you with one of them.

Panther Brown Tdi Volvo Shooting Brake Manual Miata RWD Wagon Stole HondaBro's Accord. > Frank Grimes
03/01/2016 at 20:01

you make me glad I don’t have 8th grade algebra.

You can tell a Finn but you can't tell him much > Frank Grimes
03/01/2016 at 20:01

P + C = 28

4P + 2C = 72

It requires two equations that need to be solved simultaneously.

oahz > Frank Grimes
03/01/2016 at 20:02

c = chicken p = pigs

total of both : c + p = 28

total of legs : 2c + 4p = 72

use substitution

ttyymmnn > Frank Grimes
03/01/2016 at 20:03

None, because we’re having a BBQ. That means the more pertinent questions are: How many people can we feed? How much sauce do we need? Who’s bringing the beer?

You see, math doesn’t have to be hard. It can also be tasty.

ttyymmnn > You can tell a Finn but you can't tell him much
03/01/2016 at 20:04

Okay, then what?

Frank Grimes > djmt1
03/01/2016 at 20:04

There are two maths one is what i knew before and now taking math courses I am learning the second correct one.

Frank Grimes > Panther Brown Tdi Volvo Shooting Brake Manual Miata RWD Wagon Stole HondaBro's Accord.
03/01/2016 at 20:06

I am in 16th grade not 8th.

Frank Grimes > You can tell a Finn but you can't tell him much
03/01/2016 at 20:07

I got this far but then my brain stopped working on what came next.

ttyymmnn > Panther Brown Tdi Volvo Shooting Brake Manual Miata RWD Wagon Stole HondaBro's Accord.
03/01/2016 at 20:07

I have enough trouble with my son’s 7th grade homework, let alone my other boys’ 4th grade homework.

CounterTorqueSteer > ttyymmnn
03/01/2016 at 20:07

Solve the first equation for c (or p) and the plug that into the second equation. Solve the second equation.

bob and john > Frank Grimes
03/01/2016 at 20:07

P+C = 28
P = 28-C
4P +2C = 72
4 (28 - c) +2 c = 72
112 - 4c+ 2c = 72
40 = 2c
C = 20
P = 28-C = 28-20=8

C=20
P=8

TheHondaBro > Frank Grimes
03/01/2016 at 20:08

Dafuq

Berang > Frank Grimes
03/01/2016 at 20:08

http://www.kongregate.com/forums/35-drea…

I couldn’t solve it without google.

Frank Grimes > ttyymmnn
03/01/2016 at 20:08

But there can’t be a BBQ without brisket.

XJDano > Frank Grimes
03/01/2016 at 20:09

(X*2)+(y*4)=72

I have no idea.

ttyymmnn > Frank Grimes
03/01/2016 at 20:10

That’s what the cows are for.......

djmt1 > ttyymmnn
03/01/2016 at 20:10

C=28-P

Therefore

4P + 2(28-p)=72

= 4P + 56 -2p

= 2P + 56 = 72

2P = 16

P = 8

I think. Been along time since I had to some actual maths.

E92M3 > Frank Grimes
03/01/2016 at 20:11

(X×4)+(Y×2)=72

28-Y=X

lone_liberal > Frank Grimes
03/01/2016 at 20:11

C=28-P

4P+2(28-P)=72

ttyymmnn > CounterTorqueSteer
03/01/2016 at 20:11

But how can I solve the first one with two unknowns?

iSureWilll > Frank Grimes
03/01/2016 at 20:11

C + P = 28

2C + 4P = 72

2 legs per chicken. 4 legs per pig. Unless you think they have 2 legs and 2 arms.

I've actually always been bad at these kind of problems with 2 variables so...

CounterTorqueSteer > ttyymmnn
03/01/2016 at 20:12

Kinja'd!!!

CounterTorqueSteer > Frank Grimes
03/01/2016 at 20:13

Kinja'd!!!

ttyymmnn > djmt1
03/01/2016 at 20:13

Ah yes. That seems to make sense. Algebra is one of those things that I enjoy seeing work, but I don’t necessarily want to know how to make it work. I’m a musician. I only have to count to 3 to play music.

ttyymmnn > CounterTorqueSteer
03/01/2016 at 20:15

djmt1 already walked me through it. My mind doesn’t make those sorts of leaps. The solution makes beautiful sense, but I wouldn’t have known how to get there.

CounterTorqueSteer > Frank Grimes
03/01/2016 at 20:16

Kinja'd!!!

gin-san - shitpost specialist > CounterTorqueSteer
03/01/2016 at 20:25

It’s been so long that there was a second of hesitation when I saw it but I realized that I can still do this.

I remember I was fine with basics like this, but when I got to university and started integrals I became completely lost. I passed math but still have no idea what integrals are good for. I was really good at differentials, although I can’t remember what good those were anymore.

Basically, I was strong in math in high school and catastrophically bad at it afterwards.

You can tell a Finn but you can't tell him much > ttyymmnn
03/01/2016 at 20:26

What Token Liberal said. Solve one for P or C, then use that in the other equation. Then once you have a number for P or C use that to solve for the one you don't know.

Dr. Zoidberg - RIP Oppo > Frank Grimes
03/01/2016 at 20:27

Substitution method bro. Solve for P, as an example, in one equation as a function of C and plug it into your other equation.

Or use a graphing calculator as use rref (3x2 matrix of coefficients)

TheRealBicycleBuck > lone_liberal
03/01/2016 at 20:35

Can’t believe I starred a liberal....

TheRealBicycleBuck > Frank Grimes
03/01/2016 at 20:38

My kids went through a phase where they were being taught to estimate the answer instead of just running the calculations the old fashioned way. Confusing as hell.

I taught them how to do it the old-fashioned way and their grades improved dramatically.

Frank Grimes > TheRealBicycleBuck
03/01/2016 at 20:42

How I solved it was by estimating.

There are a lot of tricks to doing math stuff but I find its just more crap I have to memorize and prefer just learning it the old school way.

samssun > ttyymmnn
03/01/2016 at 20:44

P = 28 - C so 4(28-C) + 2C = 72

112 -2C = 72 so C = 20, P = 8

The Snowman > ttyymmnn
03/01/2016 at 20:47

C=28-p

C=36-2p

28-p=36-2p

28=36-p

P=8

C=20

Frank Grimes > lone_liberal
03/01/2016 at 20:53

This checks out. But how did you see that this expression is the one?
I know P=pig and the 4 is how many legs and # of chickens is 28-pigs

But how did you form your expression from the word problem?

Frank Grimes > TheHondaBro
03/01/2016 at 20:54

college bro.

Frank Grimes > Dr. Zoidberg - RIP Oppo
03/01/2016 at 20:56

rref (x2 matrix of coefficients)

What is this wizardry? Also all those other things you said.

Phyrxes once again has a wagon! > Frank Grimes
03/01/2016 at 21:07

Algebra II teacher checking in, but I am not really a math teacher I just play one on TV. I primarily teach physics.

Equation 1 number of animals:

Pigs + Chickens = 28 so P + C =28

Equation 2, number of feel:

4 for a pig and 2 for a chicken so 4P +2C = 72

Substitution or elimination pick one, pretending the matrix stuff doesn’t exist.

Solving equation 1 for P gives us:

P = 28-C

Substituting that in for P in equation 2 gives us:

4(28-C) +2C = 72

Now for the dreaded simplify, combine like terms and solve.

Distributing the 4 gives us:

112 - 4c +2C = 72

Combing like terms gives us:

-2C = -40

Solving for C we get 20. Now drop this back in equation 1 and find the number of Pigs.

Feel free to drop me a message if you want the elimination or matrix solution.

bobbe17 > gin-san - shitpost specialist
03/01/2016 at 21:11

If you think about it in a graph it makes sense. If you have a curve, the derivative gives you the slope of the line, the integral gives you the area under the curve.

BJ > Frank Grimes
03/01/2016 at 21:11

The equation is formed from the word problem using what’s known: the total number of legs, the types of animals, and the # of legs for each type of animal.

72 legs

4 legs per pig

2 legs per chicken

Let P represent the unknown quantity of pigs, and let C represent the unknown quantity of chickens.

72 legs = 4 legs*P + 2 legs*C

When the units are the same on all elements, they can be ignored.

72 = 4P + 2C

And the rest you’ve already seen.

lone_liberal > Frank Grimes
03/01/2016 at 21:23

A farmer has chickens and pigs that total 28. So P+C=28.

There are a total of 72 Legs. Given that a chicken has two legs and a pig four you get the number of pigs times 4 (the number of legs they have) plus the number of chickens times 2 (the number of legs they have) coming to 72. 4P+2C=72. Solve the first equation for C then substitute it in to the second equation and solve for P.

Panther Brown Tdi Volvo Shooting Brake Manual Miata RWD Wagon Stole HondaBro's Accord. > Frank Grimes
03/01/2016 at 21:44

Oh...

!!! UNKNOWN CONTENT TYPE !!!

Dr. Zoidberg - RIP Oppo > Frank Grimes
03/01/2016 at 21:46

Any system of equations (if the number of equations equals the number of variables) can be “put” into a matrix, really. Rref is an abbreviation for row reduced echelon form. Basically, you need to solve for the coefficient of “one” and have all equations in the form of

xPig+yChicken=z

Given that we have:

P+C=28

4P+2C=72

Look at the coefficient line. Column one will be the coefficient of P, two will be of C, and three will be of “one,” or simply the constant.

Now build your matrix:

[ 1 1 28

4 2 72]

Now you can use functions for matrices on your calculator, namely, rref. It solves system of equations, when possible, as long as again we have n equations per n variables (as long as there is no dependent variable... lets not go there now).

But on these little systems, you should know how to do it shorthand before you use a calculator.

Dr. Zoidberg - RIP Oppo > TheHondaBro
03/01/2016 at 21:49

Please change your photo

TheHondaBro > Dr. Zoidberg - RIP Oppo
03/01/2016 at 21:58

Done

Dr. Zoidberg - RIP Oppo > TheHondaBro
03/01/2016 at 22:00

Dammit Harold!

Van Man, rocks the Man Van > Frank Grimes
03/01/2016 at 22:22

8 pigs, 20 chickens (8 x 4 = 32 and 2 x 20 = 40 and 32 + 40 = 72)

Just set up a system (x + y = 28 and 2x + 4y = 72) and solve. I did it in my head using elimination. Didn't even check the comments yet.

(This has been the Official That Guy answer, provided by Van Man)

Van Man, rocks the Man Van > lone_liberal
03/01/2016 at 22:25

I found elimination to be much easier. Multiply the first equation so that 2x (or 2C) appears in both equations, then subtract the equations to get a really easy one and find the answer. It seems simpler, and I was able to do it in my head.

Frank Grimes > Van Man, rocks the Man Van
03/01/2016 at 22:31

I have come to terms with the fact I was never and may never be gifted or talented at math.

Van Man, rocks the Man Van > Frank Grimes
03/01/2016 at 22:33

I'm the opposite. I love math and science and really don't like history or English. Math comes very easily to me but I can't write at all.

Frank Grimes > CounterTorqueSteer
03/01/2016 at 22:37

this is what I did but I struggle with translating a word problem into a expression.

ttyymmnn > Frank Grimes
03/01/2016 at 22:38

Oh. I saw C for chickens and thought C for cows. I cannot into math. At. All.

Frank Grimes > gin-san - shitpost specialist
03/01/2016 at 22:42

I am apocalyptically bad at math scienceticians should study me. I always get hung up on the words and language which makes no sense.

This happened today.

Teacher:“Take 3 out of 15 and what do you have?”
Me: “12"
Teacher: “no you have 5.”
Me: “you mean divide 15 into 3 because what you said made no sense.”

She kept saying this over and over. Taking 3 out of something doesn’t even make sense but I have learned enough math speak to understand it usually means subtraction.

Frank Grimes > ttyymmnn
03/01/2016 at 22:45

Ohhhhhhhhh...but we only have 8sqft worth of cows and they are on a train from Massapequa and there are two stops and jim has to divide his apples up before he can deliver them.

Frank Grimes > Van Man, rocks the Man Van
03/01/2016 at 22:51

I get hung up a lot on the details of things which for art is a very good thing but when you ask your teacher why a lot they get very mad. I don’t have faith in math but was always very good at reading and language and crap like that. I think I tested at like college senior level reading and comprehension when a senior in high school and I still get caught up when math people say things that makes no sense in language.

lone_liberal > Van Man, rocks the Man Van
03/01/2016 at 22:55

Interesting. I’ve never been taught that method, does it stay doable as the equations get more complex?

Van Man, rocks the Man Van > lone_liberal
03/01/2016 at 22:57

I don’t know honestly, I haven’t tried it, but it seems like it should.

X37.9XXS > Frank Grimes
03/02/2016 at 09:24

Simple

Kinja'd!!!

Your teacher complains, sue for religious bias

gin-san - shitpost specialist > Frank Grimes
03/02/2016 at 10:53

In that scenario, I place the blame on the teacher; My interpretation of the question is the same as yours. That's a really silly way of phrasing a subtraction problem.

Frank Grimes > gin-san - shitpost specialist
03/02/2016 at 13:26

i think using another word for a technical term is unhelpful and confusing in a classroom setting. The fact word problems have to be translated to math words makes me angry.

Jdrentarol > Dr. Zoidberg - RIP Oppo
03/04/2016 at 20:48

Harold?

Dr. Zoidberg - RIP Oppo > Jdrentarol
03/04/2016 at 21:23

Google Harold Slovinksi

Jdrentarol > Dr. Zoidberg - RIP Oppo
03/05/2016 at 06:39

HondaBro is named HAROLD!?!?!?!

Dr. Zoidberg - RIP Oppo > Jdrentarol
03/05/2016 at 11:00

Jdrentarol > Dr. Zoidberg - RIP Oppo
03/05/2016 at 13:18

I don’t get anything anymore