Systems of Inequalities

[mathland]

A person plans to invest up to 20,000 dollars in two different interest-bearing accounts. Each account must contain at least 5,000 dollars. The amount in one account is to be at least twice the amount in the other account. Write and graph a system of inequalities that describes the various amounts that can be deposited in each account.

Solution:

Let x = first account

Let y = second account

The words "up to" tells me to use less than or equal to when adding the two accounts.

The words "at least" tells me to use greater than or equal to as a second inequality in the system.

One of the inequalities is x + y < = 20,000.
I think the following two inequalities are also part of the systems of inequalities I must find:

x >= 5,000

y >= 5,000

I somehow think there is one more inequality missing. Stuck here...

 

[Prove It]

The amount in one account is to be at least twice the amount in the other account.

$y \geq 2\,x $

 

[jonah1]

Beer soaked ramblings follow.

$y \geq 2\,x $

You should have just let him figure that out for himself.
He'll be back for more.

 

[mathland]

$y \geq 2\,x $

Thank you. What information in the problem led you to this inequality?

 

[skeeter]

Thank you. What information in the problem led you to this inequality?

you’re kidding, right?

https://mathforums.com/threads/systems-of-inequalities.355103/post-640472
https://mathforums.com/threads/systems-of-inequalities.355103/post-640477

 

[jonah1]

Beer soaked ramblings follow.

The amount in one account is to be at least twice the amount in the other account.

$y \geq 2\,x $

Thank you. What information in the problem led you to this inequality?

you’re kidding, right?

https://mathforums.com/threads/systems-of-inequalities.355103/post-640472
https://mathforums.com/threads/systems-of-inequalities.355103/post-640477

Work induced amnesia. Probably. Maybe. Or he just wants a discussion to satisfy his fix for one.

 

[mathland]

you’re kidding, right?

https://mathforums.com/threads/systems-of-inequalities.355103/post-640472
https://mathforums.com/threads/systems-of-inequalities.355103/post-640477

Wish I was but no pun intended.

 

[topsquark]

Thank you. What information in the problem led you to this inequality?

It astounds me that you had to ask this question when you recently posted about that quintic equation. Try to stick to one level of Mathematics. Learning works better that way.

-Dan

 

[mathland]

It astounds me that you had to ask this question when you recently posted about that quintic equation. Try to stick to one level of Mathematics. Learning works better that way.

-Dan

I found the quintic equation on FB. I had no idea the actual question is beyond precalculus.

 

[topsquark]

I found the quintic equation on FB. I had no idea the actual question is beyond precalculus.

Just out of curiosity...

There is no general formula for a quintic. Can you post what you found?

-Dan

 

[mathland]

Just out of curiosity...

There is no general formula for a quintic. Can you post what you found?

-Dan

The original question was removed from the math group.

Here it is:

Solve for x∈ℤ.

x^5-15x^3-x-60 = 0

 

[topsquark]

The original question was removed from the math group.

Here it is:

Solve for x∈ℤ.

x^5-15x^3-x-60 = 0

Oh. Okay. You already posted that problem elsewhere. Thanks.

-Dan

 

[mathland]

Oh. Okay. You already posted that problem elsewhere. Thanks.

-Dan

I am not going to post so many problems. I can see that it does not matter if I show my work or not. Members do not want me to bombard the site with math questions in a MATH FORUM.

 

[jonah1]

Beer soaked non sequitur ramblings follow.

I am not going to post so many problems. I can see that it does not matter if I show my work or not. Members do not want me to bombard the site with math questions in a MATH FORUM.

I should join an aerobics class.

 

[topsquark]

I am not going to post so many problems. I can see that it does not matter if I show my work or not. Members do not want me to bombard the site with math questions in a MATH FORUM.

It has nothing to do with that. I mistakenly thought I was reading another thread by you is all.

-Dan

 

[mathland]

It has nothing to do with that. I mistakenly thought I was reading another thread by you is all.

-Dan

Ok.

 

[HOI]

The problem I have is that the first post defines x and y by
"Let x = first account

Let y = second account"
without saying how to distinguish the "first account" from the "second account".

That is especially important because of the condition that "The amount in one account is to be at least twice the amount in the other account." THAT is what we need to distinguish the two accounts.

I would have said "Let y be the amount in the LARGER account and let x be the amount in the SMALLER account".

That is what we need to establish that $$y\ge 2x$$, not $$x\ge 2y$$.