In most cases, high-speed rail travel is time- and cost-competitive with air travel when distances do not exceed 500 to 600 km (310 to 370 mi), as airport check-in and boarding procedures may add as many as two hours to the actual transit time. [7] Also, rail operating costs over these distances may be lower when the amount of fuel consumed by an airliner during takeoff and climbout is considered. As travel distance increases, the latter consideration becomes less of the total cost of operating an airliner and air travel becomes more cost-competitive.

In early afternoon, four armed men hijack a subway train in Manhattan. They stop on a slight incline, decoupling the first car to let the rest of the train coast back. Their leader is Ryder; he connects by phone with Walter Garber, the dispatcher watching that line. Garber is a supervisor temporarily demoted while being investigated for bribery. Ryder demands $10 million within an hour, or he'll start shooting hostages. He'll deal only with Garber. The mayor okays the payoff, the news of the hostage situation sends the stock market tumbling, and it's unclear what Ryder really wants or if Garber is part of the deal. Will hostages, kidnappers, and negotiators live through this? Written by <jhailey@>

The arithmetic mean of a population , or population mean, is denoted * μ* . The sample mean (the arithmetic mean of a sample of values drawn from the population) makes a good estimator of the population mean, as its expected value is equal to the population mean (that is, it is an unbiased estimator ). The sample mean is a random variable , not a constant, since its calculated value will randomly differ depending on which members of the population are sampled, and consequently it will have its own distribution. For a random sample of * n* observations from a normally distributed population, the sample mean distribution is normally distributed with mean and variance as follows: