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[主观题]

An established method of analysis for chlorinated hydrocarbons in an air sample has a mean of 12.5 m

g/m³and a standard deviation of 0.030mg/m³．

(1)Calculate the 95% confidence interval of mean of four measurements obtained by this method．

(2)How many measurements should be made if the 95% confidence interval of mean is to be 12.5mg/m³±0.017mg/m³．

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发布时间：2022-12-03

更多“An established method of analysis for chlorinated hydrocarbons in an air sample has a mean of 12.5 m”相关的问题

第1题

The publication of ____ established Emerson as the spokesman of Transcendentalism.

A.Nature

B.Self-reliance

C.The American Scholar

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第2题

A nature reserve has been established in this area where hunting ______(forbid).

A nature reserve has been established in this area where hunting ______（forbid).

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第3题

The Yellowstone National Park was established in 1908 by President Theodore Roosevelt.()

The Yellowstone National Park was established in 1908 by President Theodore Roosevelt.（)

A.错误

B.正确

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第4题

As early as 1647 Ohio made a decision that free, tax-supported schools must be established

in every town ______ 50 households or more.

A．having

B．to have

C．to have had

D．having had

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第5题

As early as 1647 Ohio made a decision that free,

tax-supported schools must be established in every town __________ 50 households or more.

A) having B) to have C) to have had D) having had

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第6题

These young adults established a trend of early marriage and relatively large familie

s that went for more than two decades and caused a major but temporary reversal of long-term demographic patterns.(语法上正确与否) ()

T.对

F.错

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第7题

It is Henry Ford's belief that ______.A．products should be made with less cost but higher

It is Henry Ford's belief that ______.

A．products should be made with less cost but higher efficiency

B．products should be sold at low prices in large quantity

C．products should be sold at high prices in large quantity

D．standards must be established in his plants

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第8题

It can be inferred that________． A.Henry Ford always tried toavoid wasteB.Henry Ford requi

It can be inferred that________．

A.Henry Ford always tried toavoid waste

B.Henry Ford required totalobservation once the standards were established

C.Henry Ford alwaysencouraged his workers to make changes of the products

D.Henry Ford made hisownDesigns of his cars

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第9题

It can be inferred that ______.A．Henry Ford always tried to avoid wasteB．Henry Ford requir

It can be inferred that ______.

A．Henry Ford always tried to avoid waste

B．Henry Ford required total observation once the standards were established

C．Henry Ford always encouraged his workers to make changes oft he products

D．Henry Ford made his own designs of his cars

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第10题

Elephants are perhaps the only animals that are hunted for their teeth. Elephant's tusks,

or very large teeth growing on either side of their mouths, are composed of a valuable material called ivory(象牙).

(77) An elephant uses its long, pointed tusks as tools for digging in the ground for food. He also uses them as weapons in combat.

The tusks of male elephants are usually large and heavy. In Africa, female elephants have long, light tusks. In India and other parts of southern Asia, female elephants have small, short tusks or none at all.

(78) Tusks in good .condition are in great demand, and may sell for as high as two thousand dollars or more. Because of this, large numbers of elephants have been killed. Some countries have initiated (开始) methods of trying to protect elephants. They have established elephant preserves, or areas of land set aside for herds of elephants where no one is allowed to harm them. Elephants on the preserves are safe from ivory hunters.

Female elephants in India and southern Asia have ______

A．large and heavy tusks

B．small and short tusks or not any teeth at all

C．small and short tusks

D．long and light tusks

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第11题

In the old days, when schools wanted to communicate with parents, they sent a letter home.

Now, in addition to email, schools and parents can connect through social media like Twitter, Facebook and Skype. The Houston Independent School District in Texas has more than two hundred thousand students. Most of them come from lower-income families. Education Week recently reported on a digital literacy training program that the district has just started for parents. The school district with help from Microsoft has established computer training centers for parents at five of its campuses. Other schools around the country are also increasing their digital services and not just in English. Many schools provide information in Spanish and other languages. Free online translation sites can also help parents stay informed about their children s education. Some school systems also give parents online access to their children s grades and school work. Six hundred students attend Knapp Elementary School near Philadelphia, Pennsylvania. Principal Joe Mazza says almost one in five students come from Bangladesh and twelve percent from South Korea. The school diversity is clear as soon as visitors enter the building. " So if you are walking in our school lobby, you are going to see English, Bengali, Korean, Spanish and all of the Finnish in the school. Now we feel that a welcoming, bright, informative, child-centered lobby really helps parents feel welcomed, honored and respected."

Which of the following is NOT mentioned as a means for schools to communicate with parents？

A．Social media.

B．Parent meetings.

C．Letters.

D．Email.

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