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A florist sold 15 arrangements in its first month of business.  The number of arrangements sold doubled each month.
 

What was the total number of arrangements the florist sold during the first 9 months?

 Mar 6, 2018
 #1
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What you're going to want to do is something like \((15*2^0)+(15*2^1)+(15*2^2)+(15*2^3)+(15*2^4)+(15*2^5)\)\(+(15*2^6)+(15*2^7)+(15*2^8) = 7665​\). I know it's long. Hold on.

 

You're basically going to do \(1+2+4+8+...\), but you're going to multiply every number by 15 since they sold 15 arrangements in the first month.

 

I hope this explanation makes sense. ¯\_(ツ)_/¯

 Mar 6, 2018
 #2
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Use exponential growth for this one as well:

 

15 x [2^N - 1] =

15 x [2^9 - 1] =

15 x [512 - 1] =

15 x 511 =

=7,665

You can also use GS to get the same answer =7,665

 Mar 6, 2018

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