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 I Got Your Number (Posted on 2004-04-18)
Lou Zerr is trying to pick up a woman at a bar. The woman, Denise, is reluctant to give out her number, but she gives Lou a clue.

"My sister, Elise and I have the same digits in our phone numbers, just in reverse order. Elise's number is also evenly divisible by mine."

What is Denise's phone number?

(Note: this IS NOT a real exchange, as far as I know. Assume the phone number has 10 digits: 7 digit number + 3 digit area code.)

 No Solution Yet Submitted by Bob Genisot Rating: 3.6000 (5 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
 Another non-trivial solution | Comment 3 of 15 |

Denise's number: (108) 900-1089

Elise's number: (980) 100-9801

This was turned up quickly by the following Visual Basic console application program, when I specified 1000000001 as the starting number for the search. The program avoids trivial solutions. In about 9 days I should have all non-trivial solutions.

Imports System
Imports System.Runtime.InteropServices
Imports System.Math
Module Module1
Dim strNumberWork As String
Dim dblNumberWork As Double
Dim strDigitWork As String
Dim dblNumericPlace As Double
Dim strNumericPlace As String
Dim dblIntervalCount As Double
Dim dblTotalCount As Double
Dim dblSubtract3 As Double
Dim dblSubtract1 As Double
Dim dblSubtract2 As Double
Dim dblRandomNumber As Double
Dim dblTensWorkarea As Double
Dim strTensWorkarea As String
Dim dblRightmostDigit As Double
Dim strRightmostDigit As String
Dim strEndFlag As String
Dim dblBeginNumber As Double
Sub Main()
Randomize()
dblIntervalCount = 0
dblTotalCount = 0
strEndFlag = "X"
dblBeginNumber = 0
While ((dblBeginNumber = 0) Or _
(dblBeginNumber > 9999999999))
Console.WriteLine("Where shall we begin? Please enter a phone number")
End While
For Index1 As Double = dblBeginNumber To 9999999999
dblRandomNumber = Index1
' Bypass the number Tristan already found.
If dblRandomNumber = 2199999978 Then
dblRandomNumber += 1
End If
dblNumericPlace = 10000000000
dblNumericPlace += dblRandomNumber
strNumericPlace = Str(dblNumericPlace)
strDigitWork = strNumericPlace.Substring(2, 1)
dblNumberWork = (10 ^ 0) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(3, 1)
dblNumberWork += (10 ^ 1) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(4, 1)
dblNumberWork += (10 ^ 2) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(5, 1)
dblNumberWork += (10 ^ 3) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(6, 1)
dblNumberWork += (10 ^ 4) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(7, 1)
dblNumberWork += (10 ^ 5) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(8, 1)
dblNumberWork += (10 ^ 6) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(9, 1)
dblNumberWork += (10 ^ 7) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(10, 1)
dblNumberWork += (10 ^ 8) * Int(strDigitWork)
strDigitWork = strNumericPlace.Substring(11, 1)
dblNumberWork += (10 ^ 9) * Int(strDigitWork)
dblIntervalCount += 1
dblTotalCount += 1
If dblTotalCount = 1 Then
Console.WriteLine("Beginning with " & _
Str(dblRandomNumber) & " " & Str(dblNumberWork))
End If
If dblIntervalCount > 9999999 Then
dblIntervalCount = 0
Console.WriteLine("So far we have examined " & _
Str(dblTotalCount) & " phone numbers")
Console.WriteLine("The last phone number we considered, " & _
"and its reverse, were: ")
Console.WriteLine(Str(dblRandomNumber) & _
" " & Str(dblNumberWork))
End If
If dblNumberWork >= dblRandomNumber Then
dblSubtract1 = dblNumberWork
dblSubtract2 = dblRandomNumber
Else
dblSubtract1 = dblRandomNumber
dblSubtract2 = dblNumberWork
End If
dblTensWorkarea = 10000000000
dblTensWorkarea += dblSubtract1
strTensWorkarea = Str(dblTensWorkarea)
strRightmostDigit = strTensWorkarea.Substring(11, 1)
dblRightmostDigit = Int(strRightmostDigit)
If (dblSubtract1 <> dblSubtract2) And _
(dblRightmostDigit <> 0) Then
While dblSubtract1 > 0
dblSubtract1 -= dblSubtract2
End While
If dblSubtract1 = 0 Then
strEndFlag = "0"
Console.WriteLine("  ")
Console.WriteLine("GOT A HIT !!!!!!!")
Console.WriteLine("HERE THEY ARE: " & _
Str(dblRandomNumber) & " " & _
Str(dblNumberWork))
While (strEndFlag <> "N" And strEndFlag <> "Y")
Console.WriteLine("  ")
Console.WriteLine("Do you wish to continue ? Y/N")
End While
End If
End If
If strEndFlag = "N" Then
Exit For
End If
Next Index1
Console.WriteLine("  ")
Console.WriteLine("Please Press Enter to End Program")
End Sub
End Module

Edited on April 19, 2004, 9:13 am
 Posted by Penny on 2004-04-19 07:08:05

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