# Write A Linear Model

nycmathguy
Homework Statement:
Write a linear model representing the situation at hand.
Relevant Equations:
y = mx + b
The average weight of a male child’s
brain is 970 grams at age 1 and 1270 grams at age 3. (Source: American Neurological Association)

Assuming that the relationship between brain weight y and age t is linear, write a linear model for the data.

I am going to start by saying y = mx + b.

Let x = t

We now have y = mt + b.

Let m = slope

m = (1290 - 970)/(3 - 1)

m = 300/2

m = 150

I say the linear model is y = 150t + (1270/970).

In short: y = 150t + 300.

Correct?

## Answers and Replies

Ibix
2020 Award
Correct?
You can check it yourself. Plug in ##t=1## and see if you get the weight at age 1 and ##t=3## and see if you get the weight at age 3.

nycmathguy and Vanadium 50
nycmathguy
You can check it yourself. Plug in ##t=1## and see if you get the weight at age 1 and ##t=3## and see if you get the weight at age 3.
Thank you. Will do.

symbolipoint
Homework Helper
Gold Member
Homework Statement:: Write a linear model representing the situation at hand.
Relevant Equations:: y = mx + b

The average weight of a male child’s
brain is 970 grams at age 1 and 1270 grams at age 3. (Source: American Neurological Association)

Assuming that the relationship between brain weight y and age t is linear, write a linear model for the data.

I am going to start by saying y = mx + b.

Let x = t

We now have y = mt + b.

Let m = slope

m = (1290 - 970)/(3 - 1)

m = 300/2

m = 150

I say the linear model is y = 150t + (1270/970).

In short: y = 150t + 300.

Correct?
This is basic Algebra 1 stuff. In case you want to review or restudy Pre-Calculus and you have lost all your skills in Algebra 1, you must review Algebra 1 from a textbook thoroughly.

nycmathguy
This is basic Algebra 1 stuff. In case you want to review or restudy Pre-Calculus and you have lost all your skills in Algebra 1, you must review Algebra 1 from a textbook thoroughly.
Wish I had the time to thoroughly review Algebra 1 and 2. The only way to do so is to STOP answering precalculus questions. Why do that? Instead of saying THIS IS BASIC ALGEBRA 1 STUFF, why not guide me along the way?

Delta2
Delta2
Homework Helper
Gold Member
Homework Statement:: Write a linear model representing the situation at hand.
Relevant Equations:: y = mx + b

In short: y = 150t + 300.

Correct?
the slope is correct but not the value of b. In order to find b correctly:
1) you know that y=150t+b
2) you know that for t=1, y=970, so what equation can you make that includes b and uses these values?

nycmathguy
the slope is correct but not the value of b. In order to find b correctly:
1) you know that y=150t+b
2) you know that for t=1, y=970, so what equation can you make that includes b and uses these values?
Let t = 1.

Let y = 970

970 = 150(1) + b

970 - 150 = b

820 = b

y = 150t + 820

Yes?

Delta2
Delta2
Homework Helper
Gold Member
Yes this is correct.

berkeman
Mentor
Wish I had the time to thoroughly review Algebra 1 and 2. The only way to do so is to STOP answering precalculus questions. Why do that? Instead of saying THIS IS BASIC ALGEBRA 1 STUFF, why not guide me along the way?
Please don't use all caps in your posts -- that is considered yelling at discussion forums and will earn you an infraction if done again.

EDIT -- Please see my update post below.

Last edited:
Delta2
berkeman
Mentor
Please don't use all caps in your posts -- that is considered yelling at discussion forums and will earn you an infraction if done again.
Upon further review of the PF rules, apparently it's only yelling in the thread title and OP. In subsequent replies I guess all caps for emphasis is allowed. Learn something new every day around here...

Fonts:
When posting a new topic do not use the CAPS lock (all-CAPS), bold, oversized, non-standard, or brightly colored fonts, or any combination thereof. They are hard to read and are considered yelling. When replying in an existing topic it is fine to use CAPS or bold to highlight main points.

nycmathguy, symbolipoint and Delta2
nycmathguy
Please don't use all caps in your posts -- that is considered yelling at discussion forums and will earn you an infraction if done again.
No one is yelling here. I simply wanted to emphasize my point of view. Read what Berkeman said about upper case letters.

berkeman
Mentor
No one is yelling here. I simply wanted to emphasize my point of view. Read what Berkeman said about upper case letters.
You mean I should re-read what I wrote?

Delta2
nycmathguy
You mean I should re-read what I wrote?
Typo.

DaveE
Gold Member
Wish I had the time to thoroughly review Algebra 1 and 2. The only way to do so is to STOP answering precalculus questions. Why do that? Instead of saying THIS IS BASIC ALGEBRA 1 STUFF, why not guide me along the way?
I think he is guiding you. Of course you don't have to listen to his advice. Of course you can invent your own curriculum. But, there is a reason that Math is broken down into a progression of subjects. Do it the way you want, but recognize that thousands of Math teachers think it's easiest to learn the basics before the more complex stuff. In any case, you're not likely to get a lot of good help if you get mad at well meaning advice, even if it's not what you want to hear.

berkeman
nycmathguy
I think he is guiding you. Of course you don't have to listen to his advice. Of course you can invent your own curriculum. But, there is a reason that Math is broken down into a progression of subjects. Do it the way you want, but recognize that thousands of Math teachers think it's easiest to learn the basics before the more complex stuff. In any case, you're not likely to get a lot of good help if you get mad at well meaning advice, even if it's not what you want to hear.
I think I can handle precalculus if guided and helped instead of all this negativity about using upper case letters, or posting in the wrong forum or writing the wrong HW Statement, etc.
Like I have said millions of times, members are not obligated to help me or anyone else. If precalculus gets to be a little too much, then I will gladly return to Algebra 1 content.

You say????

Delta2
DaveE
Gold Member
You say????
Did you come here to argue with volunteers, or to learn from their experience? That's a rhetorical question, BTW.

I say: I'm done, goodbye.

berkeman
nycmathguy
Did you come here to argue with volunteers, or to learn from their experience? That's a rhetorical question, BTW.

I say: I'm done, goodbye.
Von Voyage! I came here to learn but I think I can handle precalculus material.

symbolipoint and Delta2
symbolipoint
Homework Helper
Gold Member
I think I can handle precalculus if guided and helped instead of all this negativity about using upper case letters, or posting in the wrong forum or writing the wrong HW Statement, etc.
Like I have said millions of times, members are not obligated to help me or anyone else. If precalculus gets to be a little too much, then I will gladly return to Algebra 1 content.

You say????
I say, take another look at post #14. Some of we members believe you need to rebuild your proficiency starting with Algebra 1, and then continue on to Algebra 2; and THEN you would be ready to review Pre-Calculus. Recall the idea how these courses are linked through prerequisites? @Vanadium 50 stated the relationship very plainly.

Delta2
Homework Helper
Gold Member
I say, take another look at post #14. Some of we members believe you need to rebuild your proficiency starting with Algebra 1, and then continue on to Algebra 2; and THEN you would be ready to review Pre-Calculus. Recall the idea how these courses are linked through prerequisites? @Vanadium 50 stated the relationship very plainly.
Maybe from a more systematic point of view he would have to start with Algebra and other prerequisites. However his time is limited and he is also eager to learn calculus. So I say he just sticks with precalculus and we should be more than happy to give him some algebra lessons along the way.

nycmathguy
I say, take another look at post #14. Some of we members believe you need to rebuild your proficiency starting with Algebra 1, and then continue on to Algebra 2; and THEN you would be ready to review Pre-Calculus. Recall the idea how these courses are linked through prerequisites? @Vanadium 50 stated the relationship very plainly.
I am 56. My goal to make all the way to calculus 3. Why go back to Algebra 1 or Prealgebra, for that matter? It will take years before I get to Precalculus.

Here is the NYC public school sequence:

Prealgebra
Algebra 1
Algebra 2
Geometry
Trigonometry
Precalculus
Calculus 1
Calculus 2
Calculus 3
And so forth....

Delta2
symbolipoint
Homework Helper
Gold Member
nycmathguy posts:
I am 56. My goal to make all the way to calculus 3. Why go back to Algebra 1 or Prealgebra, for that matter? It will take years before I get to Precalculus.
No, not really. One should be able to restudy all of Algebra 1 in about 3 months. One could then restudy all of Algebra 2 (Intermediate Algebra) in 3 or 4 months; all of this on his own. Once that is accomplished then one is very likely ready to restudy all of Pre-Calculus on his own, which may take maybe 4 or 5 months, depending on study time and study schedule. If one has the time, he may then start into restudying Calculus 1, (excuse me) WITHIN ABOUT A YEAR. Maybe a little over a year to reach Calculus 1.

Your age is not a big interference. Working full-time is an interference, but if anything, it may just slow your progress. Your scheduling may be some way to keep the progress going. Most people NEED to study everyday. If skip more than one day, progress & proficiency slip. That part is not what you want to be told, but it is how this works.

nycmathguy continued saying:
Here is the NYC public school sequence:

Prealgebra
Algebra 1
Algebra 2
Geometry
Trigonometry
Precalculus
Calculus 1
Calculus 2
Calculus 3
And so forth....
That is typically a good sequence. Most people can skip the "Prealgebra". The placement of "Geometry" is flexible. One could dedicate lengthy time to it anytime after Algebra 1. Some familiarity with Trigonometry is important for studying Calculus.

symbolipoint
Homework Helper
Gold Member
Here is one of those sweaty little tips, for nycmathguy or anyone else thinking about restudying something already done earlier for credit. I have restudied all of Intermediate Algebra on my own and doing so was some of the best mathematical exercise and reading fun I had, and all while not any longer needing to worry about a letter grade - and I did so more than five times, minimum of 2 months each time.

nycmathguy
nycmathguy posts:

No, not really. One should be able to restudy all of Algebra 1 in about 3 months. One could then restudy all of Algebra 2 (Intermediate Algebra) in 3 or 4 months; all of this on his own. Once that is accomplished then one is very likely ready to restudy all of Pre-Calculus on his own, which may take maybe 4 or 5 months, depending on study time and study schedule. If one has the time, he may then start into restudying Calculus 1, (excuse me) WITHIN ABOUT A YEAR. Maybe a little over a year to reach Calculus 1.

Your age is not a big interference. Working full-time is an interference, but if anything, it may just slow your progress. Your scheduling may be some way to keep the progress going. Most people NEED to study everyday. If skip more than one day, progress & proficiency slip. That part is not what you want to be told, but it is how this works.

nycmathguy continued saying:

That is typically a good sequence. Most people can skip the "Prealgebra". The placement of "Geometry" is flexible. One could dedicate lengthy time to it anytime after Algebra 1. Some familiarity with Trigonometry is important for studying Calculus.
I will stay the course with precalculus. If I greatly struggle along the way, I will surely drop back down to algebra 1.

symbolipoint and Delta2
nycmathguy
Here is one of those sweaty little tips, for nycmathguy or anyone else thinking about restudying something already done earlier for credit. I have restudied all of Intermediate Algebra on my own and doing so was some of the best mathematical exercise and reading fun I had, and all while not any longer needing to worry about a letter grade - and I did so more than five times, minimum of 2 months each time.
Like I said, algebra 1 is not a bad idea. Let me see what happens to me in precalculus.

symbolipoint