Creating Depreciation Formula and having trouble

[rwilliams09]

So lets imagine I have in cells from left to right a bunch of numbers (let's call them investments).

Then below that I have another row showing (also from left to right) 10% of only the previous 10 years (in this case I will want the 10 previous cells from the right to the left of the row above).

Does anyone know how to do this? I am really struggling.

 

[oldbrewer]

	col B	col C
	year	investment			problem statement
	1	1000		row 5
	2	1500				determine 10% of only the last 3 years totals	3
	3	2000
	4	2500				how many years in total			5
	5	3000
						starting year for calculation			3		5-3+1
						investment in last 3 years			7500
						10%					750
							7500 obtained by
							=SUMPRODUCT(($B$5:$B$9>=$L$10)*($C$5:$C$9))

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[rwilliams09]

Thank you very much!

I think this is a little different from what I am looking for... I want to drag the same formula across about 30 cells within a row (I am using rows, not columns).

 

[oldbrewer]

2001	2002	2003	2004	2005	2006	2007	2008	2009	2010	2011	2012	2013	2014	2015	2016	2017
5000	5100	5200	5300	5400	5500	5600	5700	5800	5900	6000	6100	6200	6300	6400	6500	6600
									5450	5550	5650	5750	5850	5950	6050	6150
									5450 obtained by
									=SUM(A2:J2)/10
									dragged right

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