I need to update a spreadsheet, increasing all the values in column A as
follows:

=sum

-7.5%
+20
+5%

I've got so far : =A1*0.925+20 and this calculates the correct total to
this point

but when I try to add 5% to the end of the formula the sum fails

Also, when the new formula is calculated, how do I add it in so that it
calculates the correct sum for the whole spreadsheet

There are around 500 entries, i.e. from A1 - A500 and all these values need
to be subjected to the above calculation