SOLUTION: An orange grower finds that she gets an average yield of 40 bushels per tree when she plants 20 trees on an acre of ground. Each time she adds a tree to an acre, the yield per tree

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Question 1043672: An orange grower finds that she gets an average yield of 40 bushels per tree when she plants 20 trees on an acre of ground. Each time she adds a tree to an acre, the yield per tree decreases by 1 bushel, due to congestion. How many trees per acre should she plant for maximum yield?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +n+ = the number of trees added to 1 acre
Let +Y%28n%29+ = the yield in bushels/acre
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[ yield in bushels/acre ] = [ bushels/tree ] x [ trees/acre ]
+Y%28n%29+=+%28+40+-+n+%29%2A%28+20+%2B+n+%29+
+Y%28n%29+=+800+-+20n+%2B+40n+-+n%5E2+
+Y%28n%29+=+-n%5E2+%2B+20n+%2B+800+
The n-value of the vertex ( which is a peak )
is given by the formula:
+n%5Bmax%5D+=+-b%2F%282a%29+ when the equation has the form:
+Y%28n%29+=+a%2An%5E2+%2B+b%2An+%2B+c+
+n%5Bmax%5D+=+%28-20%29%2F%282%2A-1%29+
+n%5Bmax%5D+=+10+
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The grower started with +20+ tree/acre and adds +10+
more for max yield, so she should plant:
30 trees/acre
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check answer:
+Y%2810%29+=+%28+40+-+10+%29%2A%28+20+%2B+10+%29+
+Y%2810%29+=+30%2A30+
+Y%2810%29+=+900+
Maximum yield is 900 bushels/acre
Here's the plot:
+graph%28+600%2C+600%2C+-5%2C+50%2C+-200%2C+1200%2C+-x%5E2+%2B+20x+%2B+800+%29+