[RESOLVED] How to Find R in formula??

hi all,

am using DAO in VB6 and MS-Access as back hand.

now, i have a formula, u can find out EMI for Loan with that formula. formula is as below.

EMI = P * R * (1 + R)^N / ((1 + R)^N - 1) ----> Plz Note "R" = R/1200

Now i can find EMI through above formula in vb6.

now i want to find "R" from that.
eg. If P = 100000, N = 36 Months, EMI = 3227, R = ??
its Answer is 10 ( R = 10%)
but how can i calculate through vb6 coding.

plz. HELP me on this if possible.

thanks a lot in advance.

kaushal

There is no "nice" formula for R in terms of the remaining variables, however you can numerically compute R pretty easily using a method called "quadrature", where I'm assuming a solution exists somewhere, and the EMI function constantly increases. Hopefully these are reasonable assumptions. The following VB.NET (sorry, I don't have access to VB6 anymore) code gives R=0.008338... on your input, which agrees with the results of a numerical solver. (You said the answer should be R=10%=0.1, but I don't believe you since plugging this in directly doesn't give equality. Maybe you haven't listed some unit conversion somewhere or your numbers aren't right.)
.

VB Code:

Public Class Form1
 
    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        MessageBox.Show(FindR(3227, 100000, 36))
    End Sub
 
    Private Function FindR(EMI As Double, P As Double, N As Double) As Double
        'Use "quadrature" to find the solution
        Dim MinR As Double
        Dim MaxR As Double
        Dim MidR As Double
        MinR = 0
        MaxR = 1
        Do Until Math.Abs(MaxR - MinR) < 0.000001
            Dim TestVal As Double
 
            MidR = (MaxR + MinR) / 2
            TestVal = P * MidR * (1 + MidR) ^ N / ((1 + MidR) ^ N - 1)
            If TestVal < EMI Then
                MinR = MidR
            Else
                MaxR = MidR
            End If
        Loop
 
        Return MidR
    End Function
End Class

hi Jemidiah,

thanks a lot for ur reply and help. i solve my problem with ur suggestion.

if u read my question carefully then u find that i clearly mention there that value of "R" in formula is "R" = R / 1200. so here in ur suggestion u find R = 0.008338.
now u just have to multiply it with 1200. eg. R = 0.008338 * 1200 = "10.0056" which i mention in my question.

anyway, thanks a lot for your Help.

kaushal

Cool, glad it worked out.

While I suppose it doesn't matter, for the unit conversion you had said, "Plz Note "R" = R/1200", which I do not find at all "clear". Given your most recent post, by "R" on the left you actually meant the R which appears in your formula, and by R on the right you meant an R which does not appear in your formula. I thought you were defining a new variable "R" and not using it later, which is not the case. To be honest, this point is stupid and needlessly confusing. You should probably have just ignored the unit conversion entirely since it's irrelevant to the problem.