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#1 2006-03-03 11:46:09

Busby
Member
Registered: 2006-03-03
Posts: 1

How to calculate last years total from percentage of profits?

Having problems thinking of what the formula is for calculating the following:-

Say you you have the following:-

Gross income 2005= £8000

If this is a rise of 30% of the previous year then how would you calculate what the previous years gross was?

Same applies if it was 35% , 45% etc.

Thanks

Busby

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#2 2006-03-03 11:54:23

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,529

Re: How to calculate last years total from percentage of profits?

A rise of 30% is another way of saying it was 1.3 times larger (ie 1 + 30/100).

So the previous year was 8000/1.3 = 6153.84.

(6153.84 plus 30% = 6153.84 + 30% of 6153.84 = 6153.84 + 6153.84×0.3 = 6153.84 + 1846.15 = 7999.99)


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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#3 2006-03-03 15:26:28

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,552

Re: How to calculate last years total from percentage of profits?

If something goes down by 44% then it is 1 - 44% of 1    or    1 - .44 x 1    or    1 - .44   or 
0.56 of what you started with.

If something starts at 56 and ends at 100, then it is a 44% decrease going BACKWARDS in time, which is NOT 44% increase.   Figure out that you are adding 44 to 56, but what part of 56
is 44.  Well it is a fraction called 44  56ths of 56.  (Like 2/3's of 3 is 2) 
(or like 1/2 of 2 is 1)  ( or like 44/56 of 56 is 44)   ( or like 33333/888 of 888 is 33333)
It takes some getting used to.

Hope that doesn't just make it confusing.  smile


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