Navid,

Normally, you use the RAND function do generate random numbers. The problem
with that is that when you add something else to the spreadsheet, it
calculates a new random number. So your kids might see a line that says 3 +
4, type in 7, and the sum changes to 7 - 2.

This can be overcome like so

First, ensure cell A1 is empty and goto Tools>Options and on the Calculation
tab check the Iteration checkbox to stop the Circular Reference message.

Then in A1 add this formula: =IF($F$1="","",INT((RAND()*10+1)))

In B1 add: =IF($F$1="","",IF(INT(RAND()*2),"+","-"))

And C1 add: =IF($F$1="","",INT((RAND()*10+1)))

At this point, A1, B1 and C1 will be empty.

Copy A1:C1 down to A10:C10.

When ready to go, just put some character, say an x, in F1.

To force a reset, clear cell F1, edit cell A1:C1, don't change them,
just edit to reset to blank, copy A1:C1 down to A10:C10, and re-input F1.

As Bob mentioned, the problem is that Excel's RAND() function is
volatile.  Every change to the spreadsheet caused RAND() to be
recalculated.  I avoid that by creating MYRAND().  (I will explain how
below.)  Then create the following formulas:

A1: =int(10*myrand()+1)
B1: =if(myrand()<=0.5,"+","-")
C1: =int(10*myrand()+1)

Copy A1:C1 down through A10:C10.

Use ctrl-alt-F9 to generate a new set of random numbers.

Create MYRAND() as follows.

1. Press alt-F11 to open the VBA editor window.
2. Click Insert -> Module.
3. Enter the following text:

   function myrand()
   myrand = rnd()
   end function

4. Close the VBA editor window.

Navid

I think it is better to set the sums with a macro then they they are just
values

Sub setSums()
Dim i As Integer, tmp As Integer, op As String
'set the numbers
Range("D2:d11").ClearContents
For i = 2 To 11
Cells(i, 1) = Int(Rnd() * 10) + 1
Cells(i, 3) = Int(Rnd() * 10) + 1
'Enter the operator
x = Rnd
 If x > 0.5 Then
   Cells(i, 2) = "+"
   Else
   Cells(i, 2) = "-"
 End If
 ' make sure there are no minus answers
 'swap column C with column A
 If Cells(i, 1) < Cells(i, 3) And _
   Cells(i, 2) = "-" Then
   tmp = Cells(i, 3)
   Cells(i, 3) = Cells(i, 1)
   Cells(i, 1) = tmp
 End If

End Sub

Copy this into a VB Module (ALT + F11, Insert, Module)
Then draw a rectangle using Excel's drawing tools, right-click and choose
assign macro to the object

So you have Numb 1 in column A, operator in Column B, Numb 2 in C. The
answer goes in D. In E2 copy this formula

=IF($D2="","K",IF(AND($B2="-",$D2=A2-C2),"J",IF(AND($B2="+",$D2=$A2+$C2),"J","L")))

Copy the formula down to A11 and format the range to font Windings. This
will give a smiley face if the answer in Col  is right.

Alternatively, email peter_atherton@hotmail.com and I'll post you a workbook.

Regards
Peter

In addition to the ideas in this discussion so far, check out
http://www.tushar-mehta.com/excel/education/