Answer:
69 trees must be there this year to get the maximum yield.
Step-by-step explanation:
Let the number of trees = x.
For 90 trees, the total yield is 80 bags.
That is, the yield per tree = [tex]\frac{80}{90}=0.88[/tex]
For 80 trees, the total yield is 85 bags.
That is, the yield per tree = [tex]\frac{85}{80}=1.06[/tex]
So, For every decrease in 10 trees, the yield per trees increases by 1.06-0.88 = 0.18.
Thus, yield per tree, [tex]Y=1.06-\frac{x-80}{10}\times 0.18[/tex]
i.e. Yield per tree = [tex]Y=2.5-0.018x[/tex]
Then, the total yield, T = Number of trees(x) × Yield per tree(Y)
i.e. Total yield, T = [tex]x(2.5-0.018x)[/tex]
i.e. Total yield, T = [tex]2.5x-0.018x^2[/tex]
Now, to maximize the total yield, we will differentiate T with respect to x and equate to 0.
We get, [tex]T'=0[/tex] implies [tex]2.5-0.036x=0[/tex]
i.e. [tex]2.5=0.036x[/tex]
i.e. x= 69
Thus, 69 trees must be there this year to get the maximum yield.