Number of the day 3.59

A metal cylinder can with an open top and closed bottom is to have volume 4 cubic feet. Approximate the dimensions that require

Aleksandr-060686 [28]

Answer:

$r\approx 1.084\ feet$

$h\approx 1.084\ feet$

$\displaystyle A=11.07\ ft^2$

Step-by-step explanation:

<u>Optimizing With Derivatives </u>

The procedure to optimize a function (find its maximum or minimum) consists in :

Produce a function which depends on only one variable
Compute the first derivative and set it equal to 0
Find the values for the variable, called critical points
Compute the second derivative
Evaluate the second derivative in the critical points. If it results positive, the critical point is a minimum, if it's negative, the critical point is a maximum

We know a cylinder has a volume of 4 $ft^3$ . The volume of a cylinder is given by

$\displaystyle V=\pi r^2h$

Equating it to 4

$\displaystyle \pi r^2h=4$

Let's solve for h

$\displaystyle h=\frac{4}{\pi r^2}$

A cylinder with an open-top has only one circle as the shape of the lid and has a lateral area computed as a rectangle of height h and base equal to the length of a circle. Thus, the total area of the material to make the cylinder is

$\displaystyle A=\pi r^2+2\pi rh$

Replacing the formula of h

$\displaystyle A=\pi r^2+2\pi r \left (\frac{4}{\pi r^2}\right )$

Simplifying

$\displaystyle A=\pi r^2+\frac{8}{r}$

We have the function of the area in terms of one variable. Now we compute the first derivative and equal it to zero

$\displaystyle A'=2\pi r-\frac{8}{r^2}=0$

Rearranging

$\displaystyle 2\pi r=\frac{8}{r^2}$

Solving for r

$\displaystyle r^3=\frac{4}{\pi }$

$\displaystyle r=\sqrt[3]{\frac{4}{\pi }}\approx 1.084\ feet$

Computing h

$\displaystyle h=\frac{4}{\pi \ r^2}\approx 1.084\ feet$

We can see the height and the radius are of the same size. We check if the critical point is a maximum or a minimum by computing the second derivative

$\displaystyle A''=2\pi+\frac{16}{r^3}$

We can see it will be always positive regardless of the value of r (assumed positive too), so the critical point is a minimum.

The minimum area is

$\displaystyle A=\pi(1.084)^2+\frac{8}{1.084}$

$\boxed{ A=11.07\ ft^2}$

8 0

3 years ago

The Bobcats had a win-loss record of 41-23 before their star player, Melissa, got injured. Melissa didn’t play in any more games

MrRissso [65]

Answer:

The win percentage decreased by 10%

Step-by-step explanation:

First you need to fin the total games played right before Melissa got Injured

41+23=64

Then you need to find the win percentage by making a fraction of wins over total games

wins/total games = 41/64 = 64%

Then you need to find the number of games played after Melissa got injured

54-41 = 13 wins

34-23 = 11 losses

13+11 = 24 total games played without Melissa

You find that win percentage similarly to the first time

wins/total games = 13/24 = 54%

Then you find the difference in the percentages and there you have it!!

64% - 54% = 10%

It decreased as well therefore the answer is...

It decreased by 10%

3 0

3 years ago

. Una persona desea realizar una pintura para su próxima exposición en donde esta tenga tres colores fluorescentes y dos colores

ycow [4]

Answer: B. 350.

Step-by-step explanation:

Given: Total number of fluorescent colors = 7

Total number of pastel colors = 5

Since , he want three fluorescent colors and two pastel colors.

Number of ways to select r things out of n things = $^nC_r=\dfrac{n!}{r!(n-r)!}$

Number of ways to choose colors = $^7C_3\times\ ^5C_2$

$=\dfrac{7!}{3!4!}\times\dfrac{5!}{2!3!}\\\\=\dfrac{7\times6\times5\times4!}{3\times2\times1\times4!}\times\dfrac{5\times4\times3!}{2\times3!}\\\\=350$