Re: Can anyone solve this little problem?

Sat, 21 Apr 2007 09:30:46 GMT from Sam Bede <no-email-please@stop-
spam.com>:
I have a value, call it X. And I know it's risen over the year by a
percentage, say Y.

How do I calculate what the original value of X is?

If something rises by 15%, its new value is 1 + 15% of its old value.
15% = 15/100, so the new value is (1 + 15/100) times the old value,
or (1 + 0.15) times the old value, or 1.15 times the old value.

Your value rose by Y%, so the new value is (1 + Y/100) times the old
value Let's call the old value V. Then you have
(1 + Y/100) * V = X
You know X and Y and you want to know V.

Divide:
V = X / (1 + 100/Y)

Now plug and chug. Example: X = 1100 pounds, Y = 20%. Then
1 + 100/Y = 1.20
V = 1100 pounds / 1.20 = about 916.67 pounds

Check: 20% of 916.67 is 183.33. Adding the amount of increase to the
original gives 916.67+183.33 = 1100.00.

--
Stan Brown, Oak Road Systems, Tompkins County, New York, USA
http://OakRoadSystems.com/
.