Answer:
Manufacturers has to produce 63 DVD/Blu-Ray players to achieve a minimum cost of $644
Step-by-step explanation:
The cost equation is given as:

This is a quadratic equation in general form, which is:

Matching, we can say:
a = 0.04
b = -5
c = 800
The minimum occurs at 
and the minimum value would be to place that "x" value into the equation.
First, we find the minimum using values of a and b:

Plugging this into original, we get:

Rounding off to nearest whole number, we can say:
Manufacturers has to produce 63 DVD/Blu-Ray players to achieve a minimum cost of $644
We are given that there are a total of 78 students. If we set the following variables:

Then, the sum of all of these must be 78, that is:

Since there are 15 in chemistry and physics and 47 in chemistry, we may replace that into the equation and we get:

Simplifying:

Now we solve for P by subtracting 62 on both sides:

Therefore, there are 16 students in physics
Answer:
P in terms of V is:
P = 432/V
Step-by-step explanation:
We know that y varies inversely as x, we get the equation
y ∝ 1/x
y = k/x
k = yx
where k is called the constant of proportionality.
In our case,
P is inversely proportional to V
Given
P = 18
V = 24
so
P = k/V
k = PV
substituting P = 18 and V = 24 to determine k
k = 18 × 24
k = 432
now substituting k = 432 in P = k/V
P = 432/V
Therefore, P in terms of V is:
P = 432/V
5, because y = mx + b is the equation, with m being the slope and b being the y-intercept.
Brainliest please!