How to copy specific rows from DataTable to another one

I want to copy some rows of data table, to another one. I tried this code :

 DataTable Result = new DataTable();

    for(int i = 5; i < PageSize && i < TransactionDataTable.Rows.Count ; i++)
    {
        DataRow dr = (DataRow)TransactionDataTable.Rows[i];

        Result.ImportRow(dr);
    }

    string MobileNumber = TransactionDataTable.Rows[0]["MobileRegistration_MobileNumber"].ToString();
    string MobileNumber2 = Result.Rows[0]["MobileRegistration_MobileNumber"].ToString();

TransactionDataTable is a dataTable with more than 1000 rows.

in above code, MobileNumber has proper vallue, but MobileNumber2 dosent have. I got this error in last line ( in assigning MobileNumber2 value) :

Additional information: Column 'MobileRegistration_MobileNumber' does not belong to table .

It seems that the rows didnt copy properly, in Result dataTable.

whats the wrong with this code?

and I tried Result.Rows.Add(dr); instead of Result.ImportRow(dr); but an exception throw with this information:

This row already belongs to another table.

Thanks for any helping...