

Subject:
Math equation
Category: Science Asked by: smartstuff1282ga List Price: $8.00 
Posted:
17 Jun 2006 12:15 PDT
Expires: 17 Jul 2006 12:15 PDT Question ID: 738965 
What is the solution to this question or equation. I=NE/(NR+E) Solve for N. Assuming the numbers have no numerical value How can I isolate N by it self so N=answer? 

Subject:
Re: Math equation
Answered By: answerguruga on 17 Jun 2006 12:53 PDT 
Hi smartstuff1282ga, Here are the steps required to solve this equation: I=NE/(NR+E) 1. Move the RHS denominator to the left: I*(NR+E) = NE 2. Distribute I: INR+IE = NE 3. Collect all the terms with N in them: IE = NE  INR 4. Factor out N N*(E  IR) = IE 5. Divide through by (EIR) to solve for N N = IE/(EIR) So the final answer is: N = IE /(EIR) Hopefully that helps. Cheers! answerguruga 

Subject:
Re: Math equation
From: qed100ga on 17 Jun 2006 20:17 PDT 
An alternate route for this problem can be: I = NE/NR+E 1/I = NR/NE + E/NE 1/I = R/E + 1/N I = E/R + N I  E/R = N 
Subject:
Re: Math equation
From: brix24ga on 18 Jun 2006 03:36 PDT 
It's always nice to see an alternative approach. However, I believe that the step in going from 1/I= R/E + 1/N to I = E/R + N is in error. It can be easier to see this with an example, e.g., let I=2, R=3, E=4, and N=4. 1/I= R/E + 1/N becomes 1/2 = 3/4 + 1/(4) (which is true) but I = E/R + N becomes 2=4/3 + (4) (which is not true). I think that this step needs to be restated for the alternative approach to work. 
Subject:
Re: Math equation
From: qed100ga on 18 Jun 2006 12:17 PDT 
"However, I believe that the step in going from..." Yes, I see that you're correct about that. 
Subject:
Re: Math equation
From: brix24ga on 18 Jun 2006 14:06 PDT 
qed100, Thanks for not being defensive. "To err is human"  and I can't begin to tell you how many mistakes I've made. From another perspective, you should know that I've learned much from your comments  I'm impressed by your knowledge. 
Subject:
Re: Math equation
From: simetricalga on 30 Jul 2006 22:31 PDT 
> An alternate route for this problem can be: > I = NE/NR+E > 1/I = NR/NE + E/NE > 1/I = R/E + 1/N > I = E/R + N > I  E/R = N In addition to the mistake pointed out by brix24ga, it's important to note that you can *never* divide by a variable without considering whether it's equal to zero. Your first step assumes that I and NE are both nonzero, which may not be true. The Answerer did divide by EIR, but notice that if EIR = 0 (> E = IR), the problem has no solution anyway: I = NE/(NR+E) I = NIR/(NR+IR) = NIR/R(N+I) = NI/(N+I) I(N+I) = NI NI + I^2 = NI It's impossible to isolate N in this system of equations, so it doesn't really matter if you assume E = IR: you're only looking for what N equals where it's defined. 
Subject:
Re: Math equation
From: frodo2366ga on 27 Sep 2006 21:29 PDT 
First, it you have to ask, don't go into math. Second, first answer is right. Third, if E =IR there is no solution. Forth, see the brackets in the original equations...... 
Subject:
Re: Math equation
From: imbloga on 28 Sep 2006 20:59 PDT 
>Subject: Re: Math equation >From: frodo2366ga on 27 Sep 2006 21:29 PDT >First, it you have to ask, don't go into math. That's a fairly harsh comment to make. Irrelevant too, seeing as the asker never made any comment regarding going into math in the first place. >Second, first answer is right. >Third, if E =IR there is no solution. Not strictly true. If E and I are both zero and R nonzero, there are an infinite number of solutions for N. >Forth, see the brackets in the original equations...... 
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