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Dmitriy789 [7]
3 years ago
14

A medical researcher studies the correlation between the number of hours spent at office jobs and the incidence of chronic back

ache. Which statement BEST describes why the investigation is an observational study?
A) The researcher does not use a control group.
B) The researcher does not intervene to vary conditions.
C) It is not possible to obtain a random sample of office workers.
D) It is not possible to establish a cause-effect relation between the variables.
Mathematics
1 answer:
Sati [7]3 years ago
5 0
The answer for this question is C 

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Find the product. Enter your answer in the box below as a fraction, using the slash mark (/) for the fraction bar.
MakcuM [25]

Answer:

5/7

Step-by-step explanation:

In order to multiply fractions, multiply the numerators together and multiply the denominators together - the answers will be the numerators and denominators of the product, respectively. Also, remember that 5 can also be expressed as \frac{5}{1} in fraction form since it is a whole number.

Knowing this, multiply like so:

\frac{1}{7} · \frac{5}{1}

= \frac{5}{7}

Therefore, 5/7 is the answer.

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3 years ago
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Hello!
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6 0
4 years ago
A storage box with a square base must have a volume of 90 cubic centimeters. the top and bottom cost $0.60 per square centimeter
Paul [167]

<u>Answer-</u>

<em>For </em><em>side length of 3.56 cm</em><em> and </em><em>height of 7.10 cm</em><em> the cost will be minimum.</em>

<u>Solution-</u>

Let us assume that,

x represents the length of the sides of the square base,

y represent the height.

Given the volume of the box is 90 cm³, so

\Rightarrow V=90\\\\\Rightarrow x^2\times y=90\\\\\Rightarrow y=\dfrac{90}{x^2}

As the top and bottom cost $0.60 per cm² and the sides cost $0.30 per cm². Total cost C will be,

C=\text{cost for top and bottom}+\text{cost for rest 4 sides}\\\\=(2x^2\times 0.6)+(4xy\times 0.3)\\\\=(2x^2\times 0.6)+(4x\times \frac{90}{x^2}\times 0.3)\\\\=1.2x^2+ \dfrac{108}{x}

Then,

C'=\dfrac{d}{dx}(1.2x^2+ \dfrac{108}{x})=2.4x-\dfrac{108}\\\\C''=\dfrac{d^2}{dx^2}(1.2x^2+ \dfrac{108}{x})=2.4+\dfrac{216}{x^3}

As C'' has all positive terms  so, for every positive value of x (as length can't be negative), C'' is positive.

So, for minima C' = 0

\Rightarrow 2.4x-\dfrac{108}{x^2}=0\\\\\Rightarrow 2.4x=\dfrac{108}{x^2}\\\\\Rightarrow x^3=\dfrac{108}{2.4}=45\\\\\Rightarrow x=3.56

Then,

y=\dfrac{90}{x^2}

y=\dfrac{90}{3.56^2}

y=7.10

Therefore, for side length of 3.56 cm and height of 7.10 cm the cost will be minimum.

4 0
4 years ago
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Leona [35]

Answer:

9 and 8 are linear and 10 is non linear

Step-by-step explanation:

an = dn - c

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For example, the linear number pattern of 1, 3, 5, 7, 9, … has an equation of:

an = 2n - 1.

7 0
3 years ago
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