# ex_0521 - Exercise on May.21 1 The probability density of a...

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Exercise on May.21 1. The probability density of a random variable X is given in the figure below. 1). The probability that X is at least 1.5 is A) 1/2. B) 1/4. C) 0. D) 1/3. 2).From this density, the probability that X is between 0.5 and 1.5 is 2. IQ Test Scores. Scores on the Wechsler Adult Intelligence Scale (a standard “IQ test”) for the 20 to 34 age group are approximately normally distributed with μ = 110 and σ = 25. Use the 68-95-99.7 rule to answer these questions. (a) About what percentage of people in this age group have scores above 110? (b) About what percent have scores above 160? (c) In what range do the middle 95% of all score lie? 3 . Longlife battery, a start-up company, has developed a battery pack it claims will power a car at a sustained speed of 45 miles per hour for an

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average of 8 hours. Current data indicate that the standard deviation of battery operation times before a charge is needed is 0.4 hours. Data also showed that the distribution can be assumed to be normal.
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