How do I calculate a weighted average purchase date?

Question

A farmer bought 100 kg of seed on the following dates:

20 kg on 13-may-2007 (20%)
30 kg on 4-oct-2007  (30%)
50 kg on 31-jul-2008 (50%)

How do I calculate the weighted average purchase date? I don't want weighted average age because that changes daily. I'm thinking of a specific point in time. The total days between first and last purchase is 445 days.

If you have the age for some day $d$, $a(d)$, find $d$ such that $a(d) = 0$. — shade4159, Nov 01 '13 at 22:15

score 1 · Accepted Answer · answered Nov 01 '13 at 22:26

1

Hint: If you take 13-may-2007 as day zero, he bought 30 kg on day 144 and 50 kg on day 445. How many kg-days is that? Then divide by 100 and go that many days after 13-may.

answered Nov 01 '13 at 22:26

Ross Millikan

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How do I calculate a weighted average purchase date?

1 Answers1