[Solved] Exponential growth

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[Solved] Exponential growth

Postby elvis35to05 » Fri Jan 19, 2018 5:54 pm

Hi room,
anyone have idea how do do the formula to find out:-
how to do the penny double the amount every day project. like
day 1==1 penny
day 2==2 penny
day 3== 4 penny
day 4== 8penny
day 5== 16penny
thanks in advance.
Last edited by Hagar Delest on Sat Jan 27, 2018 7:50 pm, edited 3 times in total.
Reason: tagged [Solved].
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Re: exponential growth

Postby RoryOF » Fri Jan 19, 2018 6:34 pm

In cell A1 enter 1; in cell A2 enter "=A1*2" (no quotes). Select cell A2 by clicking on it, and pull down using the little black dot on bottom right corner of the selected cell.
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Re: expotential growth

Postby keme » Fri Jan 19, 2018 6:49 pm

And if you want to enter the number of days passed, and just calculate for that day, you just ...

... oops, just a thought: Are we doing schoolwork for you?

Just in case, for starters I only give you something to tease your memory: There is a math operation that says "multiply number by itself n times". You need to find the number to multiply by itself, and the operation in question.

If you promise that you really need the answer for some other work and it is not something you are supposed to learn, you will get the solution spelled out. We'll trust your word.
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Re: exponential growth

Postby Zizi64 » Fri Jan 19, 2018 7:41 pm

penny = 2^(day-1)
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Re: Exponential growth

Postby elvis35to05 » Sat Jan 20, 2018 12:17 am

Thanks for your help,RoryOF, keme, and Zizi64, much appreciated.

keme, No its not school work lol, i,m 70yrs old next month, i was just curious about the question of if you would take a million pounds or a penny doubled for one month.
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Re: Exponential growth

Postby keme » Sat Jan 20, 2018 10:40 am

elvis35to05 wrote:Thanks for your help,RoryOF, keme, and Zizi64, much appreciated.

keme, No its not school work lol, i,m 70yrs old next month, i was just curious about the question of if you would take a million pounds or a penny doubled for one month.

Your first post, asking a typical math assignment from class, so I had to ask. Sorry that the revelation was delayed. I hope you didn't lose millions because of that. ;)
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Re: Exponential growth

Postby RoryOF » Sat Jan 20, 2018 11:19 am

elvis35to05 wrote:Thanks for your help,RoryOF, keme, and Zizi64, much appreciated.

keme, No its not school work lol, i,m 70yrs old next month, i was just curious about the question of if you would take a million pounds or a penny doubled for one month.


If you find out how to do this, please let us know!
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Re: Exponential growth

Postby elvis35to05 » Sat Jan 20, 2018 2:57 pm

Hi room
i used formula from RoryOF,
it was just a curiosity of mine, i hope i did it right.
thanks for your help.
the question was you get a penny a day doubling every day for 31 days i get
3,221,225,471. pennies
32,212,254.71 pounds
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Re: Exponential growth

Postby Lupp » Sat Jan 20, 2018 4:08 pm

Even if I double the first penny already on day 1 of january, I only get 21 474 836.48 £ at the end of 31 january. I'm feeling so poor. What did I wrong?
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Re: Exponential growth

Postby elvis35to05 » Sat Jan 20, 2018 4:23 pm

hi Lupp,
so far except for a penny you got same as me,
this is the total for 30 days but you add the amount from day 31 to what you have.
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Re: Exponential growth

Postby jrkrideau » Sat Jan 20, 2018 4:28 pm

@ Lupp
Same here. Perhaps short term exchange rate problems?
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Re: Exponential growth

Postby RoryOF » Sat Jan 20, 2018 4:33 pm

How will we spend all this money?
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Re: Exponential growth

Postby elvis35to05 » Sat Jan 20, 2018 4:36 pm

hi RoryOF ,
if only ha ha, we would have a great life.
thanks
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Re: Exponential growth

Postby Lupp » Sat Jan 20, 2018 6:41 pm

How will we spend all this money?
I would surely advertise in TV. What about "Rory for PM!"?
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Re: Exponential growth

Postby keme » Sun Jan 21, 2018 9:32 am

elvis35to05 wrote:Hi room
i used formula from RoryOF,
...
the question was you get a penny a day doubling every day for 31 days i get
...

If you add the amounts up, it is a slightly different formula. Just remove the parenthesis.
Code: Select all   Expand viewCollapse view
penny = 2^day-1

That will take care of the one-day offset and one penny difference.
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Re: Exponential growth

Postby Zizi64 » Sun Jan 21, 2018 10:00 am

elvis35to05 wrote:
Hi room
i used formula from RoryOF,
...
the question was you get a penny a day doubling every day for 31 days i get
...


If you add the amounts up, it is a slightly different formula. Just remove the parenthesis.

Code: Select all Expand view
penny = 2^day-1


That will take care of the one-day offset and one penny difference.



In my opinion the difference _is_ inside the perentheses:

penny = day^(day-1) ... if you started (with 1 penny) on the first day (day 1).
penny = day^(day) ... if you started on the 0th day.

The difference is not negligible :D
Please send me the amount of the positive difference... :D :D :D
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