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3 years ago

9

A local hardware business wishes to find out how many of the local residents would use a delivery service. They call every tenth

person in the local listings of the phone book.
Which type of sampling is used?

1 answer:

Free_Kalibri [48]3 years ago

7 0

It is systematic because they are going every tenth person, in a random manner.

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A concentric-tube heat exchanger cools hot water owing at 1 kg/s from 80C to 30C. It uses air owing at 5 kg/s to perform this co

nordsb [41]

Answer:

The log-mean-temperature-difference is 24.03⁰C

Step-by-step explanation:

First we need to know if the heat exchanger is in parallel flow or counter-flow. However, counter flow arrangement is best used to recover heat.

L.M.T.D for counter flow is given as;

$L.M.T.D =\frac{(T_h_f_1 -T_c_f_2)-(T_h_f_2 -T_c_f_1)}{2.3log[\frac{T_h_f_1 -T_c_f_2}{T_h_f_2 -T_c_f_1}]}$

where;

Thf₁ is the initial temperature of the hot fluid = 80°C

Tcf₂ is the final temperature of the cold fluid = 51.5°C

Thf₁ - Tcf₂ = 80 - 51.5 = 28.5⁰C

Thf₂ is the final temperature of the hot fluid = 30°C

Tcf₁ is the initial temperature of the cold fluid = 10°C

Thf₂ - Tcf₁ = 30 - 10 = 20⁰C

$L.M.T.D = \frac{28.5 -20}{2.3Log[\frac{28.5}{20}]} \\\\L.M.T.D = \frac{8.5}{0.3538} =24.03^oC$

Therefore, the log-mean-temperature-difference is 24.03⁰C

3 0

2 years ago

Read 2 more answers

given that BD is both the median and altitude of triangle ABC, congruence postulate SAS is used to prove that triangle ABC is wh

stira [4]

Answer:

Isosceles

Step-by-step explanation:

Consider triangle ABC, BD is the median and the altitude drawn to the side AC. This segment (BD) divide the triangle ABC into two triangles: ABD and CBD.

In these triangles:

AD=DC (because BD is the median);
∠ADB=∠CDB=90° (because BD is the altitude);
BD is common side.

Thus, by SAS postulate, triangles ABD and CBD are conruent. Congruent triangles have congruent corresponding sides. Hence, AB=CB.

If in triangle ABC, AB=BC, then this triangle is isosceles.

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3 years ago

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Evaluate the expression 6/5x when x=20

Sindrei [870]

Answer:

24

Step-by-step explanation:

6 divided by 5 times 20 =24

6/5*20= 24

7 0

2 years ago

According to the National Institute on Drug Abuse, a U.S. government agency, 17.3% of 8th graders in 2010 had used marijuana at

miskamm [114]

Answer:

The conditions for use of the normal model to represent the distribution of sample proportion are not met. He should increase the sample size until the conditions are met.

If the test is done anyway, the null hypothesis failed to be rejected.

The conclusion is taht there is not enough evidence to support the claim that the percentage is lower in this district.

Step-by-step explanation:

The conditions for use of the normal model to represent the distribution of sample proportion are not met, as the affirmative responses are less than 10.

$np=80*0.1=8$

If the test of hypothesis is done as if the conditiones were met, we know that the claim is that the percentage is lower in this district.

Then, the null and alternative hypothesis are:

$H_0: \pi=0.173\\\\H_a:\pi$

The significance level is 0.05.

The sample has a size n=80.

The sample proportion is p=0.1.

The standard error of the proportion is:

$\sigma_p=\sqrt{\dfrac{\pi(1-\pi)}{n}}=\sqrt{\dfrac{0.173*0.827}{80}}\\\\\\ \sigma_p=\sqrt{0.001788}=0.042$

Then, we can calculate the z-statistic as:

$z=\dfrac{p-\pi+0.5/n}{\sigma_p}=\dfrac{0.1-0.173+0.5/80}{0.042}=\dfrac{-0.067}{0.042}=-1.578$

This test is a left-tailed test, so the P-value for this test is calculated as:

$P-value=P(z$

As the P-value (0.057) is greater than the significance level (0.05), the effect is not significant.

The null hypothesis failed to be rejected.

There is not enough evidence to support the claim that the percentage is lower in this district.

7 0

3 years ago

In 1979, there were 2.4 million licensed registered nurses in a country. This number increased to 3.6 million in 2012. What is t

Dennis_Churaev [7]

Answer:

It is a 50% increase

Step-by-step explanation:

2.4 million /2 = 1.2 million

2.4m + 1.2m = 3.6m

50% of 2.4 is 1.2

it is a +50% increase to get from 2.4 to 3.6

6 0

3 years ago