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zapman
New Member

USA
1 Posts

Posted - 09/12/2007 : 15:28:55

Please help with these problems

1/3s+7/9=4/3s

v-4(4-v)=-2(2v-1)

9-2m/7=19

3(x-.87)-2x=4.98

1/2q-6=1/5q

.56+3.4=.26+12.4

the_hill1962
Advanced Member

USA
1438 Posts

Posted - 09/12/2007 : 15:46:54

The problems that you wrote are linear equations. It is assumed that the instructions say to "solve for the variable". There are many sites on the Web that show you techniques to solve linear equations. Try looking at some and then come back here and show us the first step in solving them (or maybe we can take one problem at a time and help you).
For example, the first step is to simplify. Your first problem is already simplified (at this point you could ask what simplifying means....)
The next step is to get the variable term separate with the constant term (each on opposite sides of the = symbol). Your first problem would start off
1/3s + 7/9 = 4/3s
-1/3s..........-1/3s
------------------
.........7/9 = 3/3s
and so on.....
Now, re-post ONE of your problems, showing use what you have done so far, and we will help. If you want to try showing work on all your problems or telling us how you started, we will help you with all of them.
By the way, your last problem doesn't have a variable in it. There is nothing to do with that problem except to say "it is not a true statement".
******I added the following comment in the AM on 09-13-07 after reading David's post where he says to multiply through by 3s.******
Also, note that if your problem #1 appears as


  1       7     4
  - s  +  -  =  - s
  3       9     3

in your textbook, then we could misinterpret your problem as being


  1       7     4
  --  +   -  =  --
  3s      9     3s

when, in fact it is


  s       7     4s
  -   +   -  =  --
  3       9      3

Edited by - the_hill1962 on 09/13/2007 07:29:04

the_hill1962
Advanced Member

USA
1438 Posts

Posted - 09/13/2007 : 07:15:26


David, obviously zapman is not a very good math student.
Therefore I think that you may have misinterpreted the problems that
he wrote.  Yes, the way he wrote #1 LITERALLY means
  1   7    4
 -- + - = --
 3s   9   3s
But looking at the other problems in general, I believe that the
problem really was intended to appear as
  1       7     4
  - s  +  -  =  - s
  3       9     3
in which he should have written it as
(1/3)s + (7/9) = (4/3)s
So, your "multiply through by 3s" is not what zapman should do.
One of my pet peeves that students in my class complain about
is that I don't allow them to slant the fraction bars and also I
don't allow them to write the variable in the "middle".
The way that I would require a student in my class to write
  1       7     4
  - s  +  -  =  - s
  3       9     3
is
  1s     7     4s
  --  +  -  =  --
   3     9      3
telling them that they don't need to write the "1" if it bothers them.
Of course, as they 'mature' in math, they can write the problem out
however they want but if they are in my class (I teach in High
School), they are NOT that 'mature' yet!  Sometimes I have some
advanced students that I do let slide by.

quote:
Originally posted by David

1. Get rid of fractions. Multiply through by 3s.

2. Expand brackets then collect like terms.

3. Multiply through by 7.

4. Expand brackets and collect like terms.

5. Multiply through by 10q.

6. ...is incorrect.

If you can't really start on any of these you need to talk to your teacher or get a tutor. So far as I know, people here help, but don't do your work for you.

Edited by - the_hill1962 on 09/13/2007 07:20:31

the_hill1962
Advanced Member

USA
1438 Posts

Posted - 09/13/2007 : 16:31:04

I agree that we shouldn't help if there is no effort shown. I also agree that 'multiplying through' by 9 is the best way to do
(1/3)s + (7/9) = (4/3)s
However, zapman appears to be at the very beginning learning how to solve equations and did not even show such a simple first step (or ask as to how to begin solving it). A beginning student must master the concept that the 'basic' way to solve a linear equation is to end up with the variable on one side and the constant on the other. So that is how I started off with it. If zapman would have stated "I am having trouble with the problem because of the fractions", then I would have told him about the 'multiply through' by 9. However, I would have done the problem the hard (if you can call it hard) way first and showed how the fractions could be cleared out by multiplying through.
zapman:


HARD WAY (have to work with fractions):
 (1/3)s + (7/9) = (4/3)s
-(1/3)x          -(1/3)s
------------------------
          (7/9) = (3/3)s   ----->    7/9 = 1s   ---->   s=7/9

EASY WAY (clear the fractions out and then solve):
Multiply through by 9
9[(1/3)s + (7/9) = (4/3)s]   ------>  3s + 7 = 12s
                                     -3s       -3s
                                     -------------
                                           7 = 9s  ----->  s=7/9

In this problem, I think there still could be an argument that either way is just as simple. I suppose if someone absolutely despises fractions and MUST avoid them, then multiply through by 9. However, it was not a difficult thing to take (1/3)s away from (4/3)s

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