is this correct?

[scarter]

Hi,

Wondered if you could check my math?

$20.00X - $12.00X - 800 - .3($20.00x - $12.00X - 800 - 20,000) =23,236.59
8x - 800 - .3 (8x - 20800) = 25,236.59
8x - 800 - 2.4x - 6240 =25,236.59
5.6X -5440 = 25,236.59
5.6 x = 30,676.59
x = 5477.96

Thinking I did something wrong?

Thanks
scarter

 

[mmm4444bot]

Wondered if you could check my math?

$20.00X - $12.00X - 800 - .3($20.00x - $12.00X - 800 - 20,000) =23,236.59

Since you did not share the original exercise, I have no way of knowing whether or not the parameters which you typed above or actually dollar amounts; however, PLEASE do not write dollar signs in an equation. Save the dollar signs for reporting your final answer (if that answer is supposed to be an amount of money).

The equation in conventional notation follows.

20x - 12x - 800 - 0.3(20x - 12x - 800 - 20000) = 23236.59

8x - 800 - .3 (8x - 20800) = 25,236.59

I see that you correctly simplified the lefthand side of the equation, but why did you change the constant on the righthand side?

8x - 800 - 2.4x - 6240 =25,236.59
5.6X -5440 = 25,236.59 ? -800 - 6240 = -7040, not -5440
5.6 x = 30,676.59
x = 5477.96

Solving the equation in blue above, I get x ? 3177.9625.

Cheers,

~ Mark

My edit: replaced my previous foolish equation (x = 0) with the correct approximation for x

 

[scarter]

Thank You Mark

 

[Loren]

I don't think that x=0 checks.

20(0) - 12(0) - 800 - 0.3(20(0) - 12(0) - 800 - 20000) = - 800 - 0.3( - 800 - 20000)= -800 - 6240 = -7040 not 23236.59

Correction made in blue.

 

[scarter]

Loren,

20 x - 12 x - 800 - .3 (20x - 12X - 800 - 20,000) =25,236.59

I made an error in the 23,236.59 it was a typo.
But what you are saying is -800 -6240 = 5440?
not 7040 like Mark said?

scarter

 

[mmm4444bot]

-800 -6240 = 5440?

Hi Scarter:

Loren and I both goofed, but my goof is bigger. (Good grief!)

Yes. You are correct in catching that arithmetic error.

-800 - 6240 = -7040

And my revised solution for the equation in blue is x ? 3177.9625

I apologize for my lack of attention; there's really no excuse for me to have not realized that zero is a ridiculous result.

(I searched for my scratch paper to see what in the heck I did to lead me to report x = 0, but I cannot locate my work. Darn it.)

Most mathematical developments proceed by making mistakes ... but not that kind!

I made an error in the 23,236.59 it was a typo.

That's okay; apparently, there are plenty of mistakes to go around for everybody.

If we change the constant on the righthand side to 25236.59, then the solution changes to x ? 3535.1054

I would double-check that, if I were you. (Heh, heh.)

Cheers,

~ Mark

 

[scarter]

Mark,

question?

-800 - 6240 = -7040

And my revised solution for the equation in blue is x ? 3177.9625 this is a good answer BUT

5.6x -7040= 25236.59
5.6 x = 18196.59
or do I add the 7040?
I get X= 3249.39 if I subtract
How did you get X=3177.9625
scarter

 

[mmm4444bot]

Loren,

... But what you are saying is -800 -6240 = 5440?
not 7040 like Mark said?

Hi Scarter:

I did not tell you to put -7040 into your solution step.

I merely pointed out that the expression which Loren typed when explaining that my initial solution is wrong is also not correct. You asked for confirmation on whether or not

-800 - 6240 = -7040 (actually, what you typed is +7040, but I assumed that that is another typo).

I replied to confirm that -800 - 6240 does indeed equal -7040.

This confirmation has nothing to do with solving your equation.

Please back up to the distribution of -0.3 across the expression (8x - 20800)

The arithmetic involving only the constant terms follows.

-0.3 * -20800 = 6240

-800 + 6240 = 5440

25236.59 - 5440 = 19796.59

Now divide by the coefficient on x.

19796.59/5.6 ? 3535.1054

Perhaps, I misunderstood your comment regarding Loren's arithmetic error.

~ Mark

 

[Loren]

I corrected my mistake.