Answer:
The oranges should be picked in 2 weeks for maximum return
Explanation:
We assume that the return of the owner is y ($)
Assume that the number of weeks the oranges should be picked to have maximum return is x (weeks). (x≥0)
If collect now, the price for each bushel is $27
As the price per bushel decrease by $1.50 per bushel each week
=> After x weeks, the price of a bushel decrease: 1.5x ($)
=> The price of 1 bushel after x weeks is: 27 - 1.5x ($)
If collect now, each tree can yield 7 bushels
As the yield increases by half a bushel per week for the next 5 weeks
=> After x weeks with x ≤ 5, each trees would yields: 7 + 0.5x (bushels)
The return = The price of each bushes × The quantity of bushels
=> ![y = (27-1.5x)(7+0.5x)](https://tex.z-dn.net/?f=y%20%3D%20%2827-1.5x%29%287%2B0.5x%29)
⇔![y= 27 (7 +0.5x) - 1.5x(7+0.5x) = 189 + 13.5x - 10.5x - 0.75x^{2}](https://tex.z-dn.net/?f=y%3D%2027%20%287%20%2B0.5x%29%20-%201.5x%287%2B0.5x%29%20%3D%20189%20%2B%2013.5x%20-%2010.5x%20-%200.75x%5E%7B2%7D)
⇔![y = -0.75x^{2} +3x +189](https://tex.z-dn.net/?f=y%20%3D%20-0.75x%5E%7B2%7D%20%2B3x%20%2B189)
We have: if the equation has the form of
with a≠0, its maximum value is: ![max y = c - \frac{b^{2} }{4a}](https://tex.z-dn.net/?f=max%20y%20%3D%20c%20-%20%5Cfrac%7Bb%5E%7B2%7D%20%7D%7B4a%7D)
In the equation
, we have: a = -0.75; b = 3; c = 189
=> ![max y = c -\frac{b^{2} }{4a} = 189 - \frac{3^{2} }{4.(-0.75)} = 189 - \frac{9}{-3} = 189 - (-3) = 189+3 = 192](https://tex.z-dn.net/?f=max%20y%20%3D%20c%20-%5Cfrac%7Bb%5E%7B2%7D%20%7D%7B4a%7D%20%3D%20189%20-%20%5Cfrac%7B3%5E%7B2%7D%20%7D%7B4.%28-0.75%29%7D%20%3D%20189%20-%20%5Cfrac%7B9%7D%7B-3%7D%20%20%3D%20189%20-%20%28-3%29%20%3D%20189%2B3%20%3D%20192)
To look for the number of weeks, we should find x (0≤x≤5) with which y = 192
![192 = -0.75x^{2} +3x +189](https://tex.z-dn.net/?f=192%20%3D%20-0.75x%5E%7B2%7D%20%2B3x%20%2B189)
⇔![-0.75x^{2} + 3x + 189 - 192 = 0](https://tex.z-dn.net/?f=-0.75x%5E%7B2%7D%20%2B%203x%20%2B%20189%20-%20192%20%3D%200)
⇔![-0.75 x^{2} + 3x - 3 =0](https://tex.z-dn.net/?f=-0.75%20x%5E%7B2%7D%20%2B%203x%20-%203%20%3D0)
⇔![-0.75x^{2} + 4*0.75x - 0.75*4 =0](https://tex.z-dn.net/?f=-0.75x%5E%7B2%7D%20%20%2B%204%2A0.75x%20-%200.75%2A4%20%3D0)
⇔![x^{2} -4x + 4 = 0](https://tex.z-dn.net/?f=x%5E%7B2%7D%20-4x%20%2B%204%20%3D%200)
⇔ ![(x-2)^{2} = 0](https://tex.z-dn.net/?f=%28x-2%29%5E%7B2%7D%20%20%3D%200)
⇔ x = 2
The oranges should be picked in 2 weeks for maximum return