My Math Forum  

Go Back   My Math Forum > College Math Forum > Linear Algebra

Linear Algebra Linear Algebra Math Forum


Reply
 
LinkBack Thread Tools Display Modes
September 2nd, 2019, 07:01 PM   #1
Newbie
 
Joined: Sep 2019
From: New york

Posts: 6
Thanks: 0

Unhappy a simple system with an impossible answer...

first post here... currently an applied math student attending Stonybrook university. The question seems so simple. But I am unable to find an answer.

jack can do 3 chemistry problems and 6 math problems an hour.
Jill can do 4 chemistry problems and 7 math problems an hour.

How long must they both work to finish 11 chemistry problems and 17 math problems?

If you solve this system, you get jack's time as (-3 hours) and Jill's is 5 hours. Obviously, this is impossible. But the only other way I found to accurately estimate this is just guessing and checking.... getting closest with jack doing 1.4 hours of study and Jill doing 1.7 ... producing 11 completed chemistry problems but 20.3 math questions.

Very confused how to approach this question efficiently without guessing. Please help!!!!

Last edited by skipjack; September 4th, 2019 at 04:36 PM.
Bioobird is offline  
 
September 2nd, 2019, 07:10 PM   #2
Senior Member
 
Joined: Aug 2012

Posts: 2,393
Thanks: 749

Quote:
Originally Posted by Bioobird View Post
first post here... currently an applied math student attending Stonybrook university. The question seems so simple. But I am unable to find an answer.
Do you know professor Lawson, or know of him? He was my prof for complex variables way back in the day at Berkeley.

https://en.wikipedia.org/wiki/H._Blaine_Lawson

Last edited by Maschke; September 2nd, 2019 at 07:20 PM.
Maschke is offline  
September 2nd, 2019, 07:28 PM   #3
Newbie
 
Joined: Sep 2019
From: New york

Posts: 6
Thanks: 0

No!!

No I don’t know him... but I have come across the term “complex variables” when trying to do some research on a problem like this.... how do you approach it???
Bioobird is offline  
September 2nd, 2019, 07:45 PM   #4
Senior Member
 
Joined: Aug 2012

Posts: 2,393
Thanks: 749

Quote:
Originally Posted by Bioobird View Post
No I don’t know him... but I have come across the term “complex variables” when trying to do some research on a problem like this.... how do you approach it???
Complex variables is calculus on the complex numbers. It's got a very different flavor than regular (real number) calculus. I don't think it bears on your problem.
Maschke is offline  
September 2nd, 2019, 07:49 PM   #5
Newbie
 
Joined: Sep 2019
From: New york

Posts: 6
Thanks: 0

I’m affluent with multivariable calculus... but linear algebra is a lot different... how do I efficiently compute the answer to this? Without putting it into a computer or something?
Bioobird is offline  
September 2nd, 2019, 08:41 PM   #6
Senior Member
 
romsek's Avatar
 
Joined: Sep 2015
From: USA

Posts: 2,553
Thanks: 1403

the thing to remember is rates add

$r_{kc}=3 ~prob/hr$
$r_{km}=6~prob/hr$

$r_{lc}=4~prob/hr$
$r_{lm} = 7~prob/hr$

$T = \dfrac{11}{r_{kc}+r_{lc}} + \dfrac{17}{r_{km}+r_{lm}} = \\

\dfrac{11}{7} + \dfrac{17}{13} = \dfrac{262}{91} ~hr \approx 2~hr~53~min$
romsek is offline  
September 3rd, 2019, 05:33 PM   #7
Newbie
 
Joined: Sep 2019
From: New york

Posts: 6
Thanks: 0

Incorrect

This system is asking for a certain number of hours for each students to work.... you need to isolate exactly how much jack needs to work and Jill separately.
Bioobird is offline  
September 3rd, 2019, 05:58 PM   #8
Senior Member
 
romsek's Avatar
 
Joined: Sep 2015
From: USA

Posts: 2,553
Thanks: 1403

Quote:
Originally Posted by Bioobird View Post
This system is asking for a certain number of hours for each students to work.... you need to isolate exactly how much jack needs to work and Jill separately.
so you want to treat it as if each works alone?

$T_{jack} = \dfrac{11}{3} + \dfrac{17}{6} = \dfrac{13}{2} = 6~hr~30~min$

$T_{jill} = \dfrac{11}{4} + \dfrac{17}{7} = \dfrac{77+68}{28}=\dfrac{145}{28} \approx 5~hr~11~min$
romsek is offline  
September 3rd, 2019, 08:32 PM   #9
Newbie
 
Joined: Sep 2019
From: New york

Posts: 6
Thanks: 0

Noo

you want to find the MINIMUM amount of time (two variables) for jack and Jill. To complete exactly 11 chemistry problems and 17 math problems. When you solve this system mathematically it yields -3 and 5 ... which doesn’t make any real world sense. I have approximated their times to be somewhere Around 1.7 hours for jack and 1.4 hours for Jill. But this was through no other means than brute force guessing and checking. Mathematically I would like to know how to approach a problem like this more efficiently...
Bioobird is offline  
September 4th, 2019, 01:02 AM   #10
Global Moderator
 
Joined: Dec 2006

Posts: 20,972
Thanks: 2222

Please clarify what system you solved, so that we know what you tried. Can jack do 3 chemistry problems and 6 math problems an hour simultaneously?

Last edited by skipjack; September 4th, 2019 at 04:37 PM.
skipjack is offline  
Reply

  My Math Forum > College Math Forum > Linear Algebra

Tags
answer, impossible, linear algebra, math, simple, simply, system, system of equations



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
A simple answer helpmeddddd New Users 4 May 5th, 2019 09:27 PM
kind of silly/simple question with probably a simple answer. GumDrop Math 4 October 4th, 2016 04:34 PM
System of Equations, missing pair of answer triplekite Algebra 3 December 7th, 2012 02:57 PM
simple system of eq mrjones Complex Analysis 4 July 2nd, 2010 08:57 AM
"IMPOSSIBLE PROBLEM" - SEE IF YOU CAN ANSWER IT [reply] s2m0i1t2h Algebra 1 November 24th, 2008 03:46 PM





Copyright © 2019 My Math Forum. All rights reserved.