"Fred Smith" <fredsmith99@yahoo.com> wrote in message
news:Otu77xgcGHA.3388@TK2MSFTNGP05.phx.gbl...

> "reckyroo" <reckyroo@discussions.microsoft.com> wrote in message
> news:B4B3D251-5650-4B39-AD3D-6FFC0DF237E5@microsoft.com...
>> Hi
>> I haven't used excel for a long time and can't remember how to so much at
>> all!
>> I need to start with a number 1, multiply it by 2, then multiply that
>> answer
>> by 2, multiply that answer by 2 and carry on multiplying my answers by 2
>> until I have done this 480 times. The answers that excel is throwing out
>> is
>> either as a decimal which is rounding it up and not giving a true answer,
>> or
>> the answer I get is 4.72237E+21 (which doesn't mean anything at all to me
>> i'm
>> afraid!)!
>> Can anybody help me to get a true calculation, without rounding up etc?
>> Any help would be much appreciated.

> 4.722371E+21 is 4.7 followed by 21 zeros, ie,
> 4,700,000,000,000,000,000,000,000,000.
>
> You should expect a number this large if you are multiplying 2 by itself
> 480 times.
>
> You can also simplify things greatly by using exponentiation. The formula
>
> =2^480
>
> will give you your answer. It's 3.1E144, so while your calculation was
> close, you missed out on a few 2's.

Missed more than a few, Fred.
4.722371E+21 is 2^72, rather than 2^480
[Note that your example showed 4.7E27, not 4.7E21]

The OP needs to realise that there will be rounding in a calculation as long
as this. Excel works to 15 significant figures, not the 145 figures that
this would need.
--
David Biddulph
Rowing web pages at
http://www.biddulph.org.uk/