Dimensional Analysis. I know my equations are right

[flyingpig]

Homework Statement

A birchwood table company has an individual who does all its finishing
work and it wishes to use him in this capacity at least 36 hours each
week. By union contract, the assembly area can be used at most 48 hours
each week. The company has three models of birch tables, T1, T2 and T3.
T1 requires 1 hour for assembly, 2 hours for finishing, and 9 board feet of
birch. T2 requires 1 hour for assembly, 1 hour for finishing and 9 board
feet of birch. T3 requires 2 hours for assembly, 1 hour for finishing and 3
board feet of birch. Write a LOP that will compute how many of each model
should be made in order to minimize the board feet of birchwood used.2. What I want to do with this problem

Here is the thing, I wrote out the equations, but my variables don't mean a thing. I tried to make some sense out of it

Here is the equations

1x_1 + 1x_2 +2x_3 \leq 48
2x_1 + 1x_2 +1x_3 \geq 36
P = 9x_1 + 9x_2 + 3x_3

x_1, x_2, x_3 \geq 0

For instance the first equation is

1x_1 + 1x_2 +2x_3 \leq 48

Right hand side is hours, so I expect the units on 1x_1 + 1x_2 +2x_3 cancel out so that it gives me hours too

Look at the coefficients of 1x_1 + 1x_2 +2x_3

The "1" in front of x_1 represents "hour for assembly" or "hour/assembly". So to make things work out, x_1 has units "assembly for T_1[/tex]"

But that doesn't work for the second equation because I will need x_1 to have units "finishing for T_1[/tex]"

 

[I like Serena]

x1 is the number of tables of type T1 that is produced per week.

For assembly, the 1 in front of x1, is the hours of assembly/table of type T1.

 

[flyingpig]

x1 is the number of tables of type T1 that is produced per week.

For assembly, the 1 in front of x1, is the hours of assembly/table of type T1.

I don't see how those units could cancel out...

x1 would change for finishing work, but I need a consistent unit

 

[Ray Vickson]

Homework Statement

A birchwood table company has an individual who does all its finishing
work and it wishes to use him in this capacity at least 36 hours each
week. By union contract, the assembly area can be used at most 48 hours
each week. The company has three models of birch tables, T1, T2 and T3.
T1 requires 1 hour for assembly, 2 hours for finishing, and 9 board feet of
birch. T2 requires 1 hour for assembly, 1 hour for finishing and 9 board
feet of birch. T3 requires 2 hours for assembly, 1 hour for finishing and 3
board feet of birch. Write a LOP that will compute how many of each model
should be made in order to minimize the board feet of birchwood used.


2. What I want to do with this problem

Here is the thing, I wrote out the equations, but my variables don't mean a thing. I tried to make some sense out of it

Here is the equations

1x_1 + 1x_2 +2x_3 \leq 48
2x_1 + 1x_2 +1x_3 \geq 36
P = 9x_1 + 9x_2 + 3x_3

x_1, x_2, x_3 \geq 0

For instance the first equation is

1x_1 + 1x_2 +2x_3 \leq 48

Right hand side is hours, so I expect the units on 1x_1 + 1x_2 +2x_3 cancel out so that it gives me hours too

Look at the coefficients of 1x_1 + 1x_2 +2x_3

The "1" in front of x_1 represents "hour for assembly" or "hour/assembly". So to make things work out, x_1 has units "assembly for T_1[/tex]"

But that doesn't work for the second equation because I will need x_1 to have units "finishing for T_1[/tex]"

If x1 is the number of pieces of T1 to produce, x1 is a dimensional number. The number of assembly hours per piece of T1 is 1, so x1 units need 1*x1 hours. Note that 1*x1 is dimensionless; the "hours" occurs outside the expression, because we take 1 as the number of hours, not a time of 1 hour. Similarly, the number of hours we have available is 48; the '48' is dimensionless. I avoided saying the available time is 48 hours, in favor of saying the number of hours available is 48. See the difference?

RGV

 

[I like Serena]

I don't see how those units could cancel out...

x1 would change for finishing work, but I need a consistent unit

How would x1 change?

For finishing work we have:
x1 is still the "number of tables of type T1"
The 1 in front of x1 is the "hours of finishing/table of type T1".

The "number of tables of type T1" cancels out, and the result is "hours of finishing".
The total "hours of finishing" is supposed to exceed 36 "hours of finishing".