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hichkok12 [17]
2 years ago
13

If you add 21 to my number and then multiply the result by 3, you will get 84 more than two-thirds of my number. Find my number.

Mathematics
1 answer:
Ksivusya [100]2 years ago
5 0

Based on the calculations, the unknown number is equal to \frac{-45}{7}

  • Let the unknown number be x.

<h3>How to find an unknown number:</h3>

Translate the word problem into an algebraic expression, we have;

Adding 21 to the unknown number:

21 +x

Multiplying the result by 3:

3\times (21+x)

84 more than two-thirds of the unknown number:

\frac{2x}{3} +84

Equating the equations, we have:

3\times (21+x) = \frac{2x}{3} +84\\\\43+3x=\frac{2x}{3} +84

Cross-multiplying, we have:

43+3x=\frac{2x}{3} +84\\\\129+9x=2x+84\\\\9x-2x=84-129\\\\7x=-45\\\\x=\frac{-45}{7}

Read more on word problems here: brainly.com/question/13170908

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An open top box is to be built with a rectangular base whose length is twice its width and with a volume of 36 ft 3 . Find the d
denpristay [2]

Answer:

The dimensions of the box that minimize the materials used is 6\times 3\times 2\ ft

Step-by-step explanation:

Given : An open top box is to be built with a rectangular base whose length is twice its width and with a volume of 36 ft³.

To find : The dimensions of the box that minimize the materials used ?

Solution :

An open top box is to be built with a rectangular base whose length is twice its width.

Here, width = w

Length = 2w

Height = h

The volume of the box V=36 ft³

i.e. w\times 2w\times h=36

h=\frac{18}{w^2}

The equation form when top is open,

f(w)=2w^2+2wh+2(2w)h

Substitute the value of h,

f(w)=2w^2+2w(\frac{18}{w^2})+2(2w)(\frac{18}{w^2})

f(w)=2w^2+\frac{36}{w}+\frac{72}{w}

f(w)=2w^2+\frac{108}{w}

Derivate w.r.t 'w',

f'(w)=4w-\frac{108}{w^2}

For critical point put it to zero,

4w-\frac{108}{w^2}=0

4w=\frac{108}{w^2}

w^3=27

w^3=3^3

w=3

Derivate the function again w.r.t 'w',

f''(w)=4+\frac{216}{w^3}

For w=3, f''(3)=4+\frac{216}{3^3}=12 >0

So, it is minimum at w=3.

Now, the dimensions of the box is

Width = 3 ft.

Length = 2(3)= 6 ft

Height = \frac{18}{3^2}=2\ ft

Therefore, the dimensions of the box that minimize the materials used is 6\times 3\times 2\ ft

4 0
3 years ago
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