How do I set it a cell so that when a certain cell's
content has been changed other cells contents change.

For example I have 20 cells that either have a 'y'
or 'n'. These 'y', or 'n' values are input manually.

There is also one cell that contains a number that is
input manually.

I would like to set it so that the 20 cell's that contain
an 'y' or 'n' value are set to 'n' when the cell that has
a number in it is changed and only when it changes.

If this is not possible how about doing the same thing
when the cell is exited?

Thanks Ben