If I add a percentage to a number, how do I find the original again?
March 6, 2010 1:18 PM   Subscribe

In Excel, adding percentages, needing to correct, and having to get back to the original amount. Can I do this?

A friend added 8% to a column of random numbers (amounts) in Excel. The next day, he found out that was supposed to add a different percentage. Looking at this row of numbers, how can he get back to his original amount? He can't just subtract 8%, because that 8% will be larger than the original.

There is no backup, and he saved and exited a day previous.

I suspect he's screwed, am I right?
posted by nevercalm to Computers & Internet (5 answers total) 1 user marked this as a favorite
Multiply the too-big numbers by 100/108 (like B1=A1*100/108 in Excelese)
posted by hexatron at 1:22 PM on March 6, 2010

a * 1.08 = b
a = b/1.08
posted by found missing at 1:23 PM on March 6, 2010

Add a new column with this formula

= n / 1.08

where n is the amount in the column you want to change back.

Copy the new column, go to the old column and select paste special. Then select "values only."

Or, what everyone else is saying...
posted by ifandonlyif at 1:29 PM on March 6, 2010

When your friend added 8% to the numbers in this column, and replaced the original numbers with the new numbers, he performed this function, in Excel-speak:

(Y x 0.08)+Y=Z

Where Z is your new number.

You're going to want to divide your column of new numbers by 1.08 in order to get your old numbers back. To do this in excel, create a new column. In your new column, enter the formula =[cell with new number]/1.08

Copy the formula all the way down. There are your old numbers.
posted by juniperesque at 1:38 PM on March 6, 2010

I love math. Thank you all.
posted by nevercalm at 1:40 PM on March 6, 2010

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