Given: C(N) = 15,000 + 8000N <span>
In the above equation simply substitute:
N(t) = 100t - 5t^2
for N
</span>
<span>Therefore:
C(t) = 15,000 + 8000{ 100t-5t^2 }
C(t) =15,000 + 800,000t - 40,000t^2.</span>
at t = 5
C(5) = 15,000 + 800,000*5
- 40,000*(5)^2
<span>C(5) = 3,015,000</span>
First set up your two equations:
x + y = 90
x = 2y - 30
Then substitute what x equals in the second equation into the first equation:
(2y -30) + y = 90
Now solve for y:
3y -30 = 90
3y = 120
y = 40
Then use y = 40 and substitute the value for y into one of your original equations and solve for x. I'll choose the first one, but either one will work.
x+ 40 = 90
x = 50
So your solution is x = 50 and y = 40
257,650 rounded to the nearest hundred is 257,700 because it is right at the border (50) we have to round up.
To solve this problem you must apply the proccedure shown below:
1. You have that 
varies jointly as 
and 
and inversely as the product of 
and 
. Therefore, you can write the following equation, where 
is the constant of proportionality:
2. Now, you must solve for the constant of proportionality, as following:
3. Susbtiute values:
4. Substitute the value of the constant of proportionality into the equation:
The answer is:
Sorry for the hand writing. But you want to factor out a 4y^2 which will result in (9y^2-1). Then you will factor out the equation in parentheses to (3y-1)(3y+1). Don’t forget to put the 4y^2 out front!
