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icang [17]
2 years ago
14

A box with a rectangular base and open top must have a volume of 128 f t 3 . The length of the base is twice the width of base.

The base needs to be stronger than the sides, so it costs more. The base costs $9 per f t 2 , while the sides only cost $6 per f t 2 . We wish to find the dimensions of the box that minimize the cost of material used.
Mathematics
1 answer:
noname [10]2 years ago
8 0

Answer:

Width = 4ft

Height = 4ft

Length = 8ft

Step-by-step explanation:

Given

Volume = 128ft^3

L = 2W

Base\ Cost = \$9/ft^2

Sides\ Cost = \$6/ft^2

Required

The dimension that minimizes the cost

The volume is:

Volume = LWH

This gives:

128 = LWH

Substitute L = 2W

128 = 2W * WH

128 = 2W^2H

Make H the subject

H = \frac{128}{2W^2}

H = \frac{64}{W^2}

The surface area is:

Area = Area of Bottom + Area of Sides

So, we have:

A = LW + 2(WH + LH)

The cost is:

Cost = 9 * LW + 6 * 2(WH + LH)

Cost = 9 * LW + 12(WH + LH)

Cost = 9 * LW + 12H(W + L)

Substitute: H = \frac{64}{W^2} and L = 2W

Cost =9*2W*W + 12 * \frac{64}{W^2}(W + 2W)

Cost =18W^2 +  \frac{768}{W^2}*3W

Cost =18W^2 +  \frac{2304}{W}

To minimize the cost, we differentiate

C' =2*18W +  -1 * 2304W^{-2}

Then set to 0

2*18W +  -1 * 2304W^{-2} =0

36W - 2304W^{-2} =0

Rewrite as:

36W = 2304W^{-2}

Divide both sides by W

36 = 2304W^{-3}

Rewrite as:

36 = \frac{2304}{W^3}

Solve for W^3

W^3 = \frac{2304}{36}

W^3 = 64

Take cube roots

W = 4

Recall that:

L = 2W

L = 2 * 4

L = 8

H = \frac{64}{W^2}

H = \frac{64}{4^2}

H = \frac{64}{16}

H = 4

Hence, the dimension that minimizes the cost is:

Width = 4ft

Height = 4ft

Length = 8ft

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Cedro bought 10 ounces of Cereal A for $2.25. Then he bought 15 ounces of Cereal B for $3.30. Which cereal is less expensive?
miv72 [106K]

Answer:

Cereal B.

Step-by-step explanation:

To figure out how much it costs per ounce for each cereal, first we need to divide.

Cereal A: $2.25 / 10 = $.225 per ounce

Cereal B: $3.30 / 15 = $.22 per ounce

So, cereal B is less expensive.

5 0
2 years ago
A man pays a total of 4800 in flat rental for 3 months. find the man monthly rental rate.
Elza [17]

Answer:

<u>1,600</u>

Step-by-step explanation:

divide the total money by the time to get unit rate such as 4800 divided by 3 equals <u>1600</u>

Also can you give brainliest to all of your questions bc it really hard to get brainliest and it be really nice you can choose who i dont really care but just please do it it helps a lot

3 0
3 years ago
Urgent help, please!.....
pishuonlain [190]

To solve this problem, we want to get all of the possible options into the same form, so that it is easier to compare them. Personally, I prefer comparing in decimals, so that is how I am going to solve this problem.


13/4 - To turn this improper fraction into its decimal equivalent, it is easier to first turn it into a mixed number by dividing the numerator by the denominator.

13/4 = 3 1/4

Because we know that 1/4 = 0.25, we now know that 3 1/4 = 3.25

Therefore, 13/4 = 3.25


3 1/2 - This is similar to the end of the process above. We know that 1/2 = 0.5, so we know that 3 1/2 = 3.5

3 1/2 = 3.5


3.15 is already in its decimal form, so we can leave that be for now.


√9 - To simplify this, we must figure out what number multiplied by itself equals 9. If we start with 2 (2*2 = 4), so that is too small. Next maybe we try 4 (4 * 4 = 16), so that is too large. Now we know we need a number in between 2 and 4, so maybe we try 3. 3 * 3 = 9, so we can conclude that √9 = 3.

√9 =3


If we take all of our decimal equivalents, we have 3.25, 3.5, 3.15, and 3.


Because all of these values have the same whole number value of 3, we need to compare the decimals to find out what order they belong in.


Our final order is (from smallest to largest): 3, 3.15, 3.25, 3.5


But, we need to substitute in the equivalent values we were given for these decimals originally to finish the problem.


This makes your final answer: √9, 3.15, 13/4, 3 1/2


Hope this helps!

4 0
3 years ago
Read 2 more answers
2. 2(x+1.25) = 3.5
dangina [55]

Answer:

x = 0.5

Step-by-step explanation:

Given

2(x + 1.25) = 3.5 ← divide both sides by 2

x + 1.25 = 1.75 ( subtract 1.25 from both sides )

x = 0.5

8 0
3 years ago
Read 2 more answers
What’s the correct answer for this?
Lynna [10]

Answer:

A.

Step-by-step explanation:

tan x= 6/8

usually tan θ = perpendicular / base

So,

we get perpendicular = 6, base = 8

Now using Pythagorean Theorem to find hypotenuse

hyp² = base² + Perp²

hyp² = 8² + 6²

hyp²= 64 + 36

hyp²=100

Taking sq root on both sides

hypotenuse = 10

Now

sin θ = Perpendicular / Hyp

sin x = 6 / 10

Now

cos θ = base / Hyp

cos x = 8 / 10

6 0
3 years ago
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