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某社区年平均5万人口，其中男性2.4万人，女性2.6万人，年内出生250人，死亡100人，其中男性55人，女性45人。 计算该社区男性年死亡率的分母是
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某市2001年人口数是100万，共登记报告肝癌患者117例，其中99例是本年新髓记患者，18例是以往的老患者。 该市肝癌的患病率为
There are few more sobering online activities than entering data into college-tuition calculators and gasping as the Web spits back a six-figure sum, But economists say families about to go into debt to fund four years of partying, as well as studying, can console themselves with the knowledge that college is an investment that, unlike many bank stocks, should yield huge dividends. A 2008 study by two Harvard economists notes that the "labor-market premium to skilr " —or the amount college graduates earned that’s greater than what high-school graduates earned—decreased for much of the 20th century, but has come back with a vengeance since the 1980s. In 2005, the typical full-time year-round U.S. worker with a four-year college degree earned $ 50,900, 62% more than the $ 31,500 earned by a worker with only a high-school diploma. There’s no question that going to college is a smart economic choice. But a look at the strange variations in tuition reveals that the choice about which college to attend doesn’t come down merely to dollars and cents. Does going to Columbia University (tuition, room and board $ 49,260 in 2007-2008) yield a 40% greater return than attending the University of Colorado at Boulder as an out-of-state student( $ 35,542) Probably not. Does being an out-of-state student at the University of Colorado at Boulder yield twice the amount of income as being an in-state students( $17,380) there Not likely. No, in this consumerist age, most buyers aren’t evaluating college as an investment, but rather as a consumer product—like a car or clothes or a house. And with such purchases, price is only one of many crucial factors to consider. As with automobiles, consumers in today’s college marketplace have vast choices, and people search for the one that gives them the most comfort and satisfaction in line with their budgets. This accounts for the willingness of people to pay more for different types of experiences(such as attending a private liberal-arts college or going to an out-of-state public school that has a great marine-biology program). And just as two auto purchasers might spend an equal amount of money on very different cars, college students(or, more accurately, their parents)often show a willingness to pay essentially the same price for vastly different products. So which is it The two Harvard economists note in their study that, for much of the 20th century, _______.
When he arrived in America, he was surprised to learn that the mayor of the city was Chinese by ______.
比较度量衡单位不同的几组资料的变异度时，用
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