2.)Light bulbs are normally distributed with an average lifetime of 1000 hours a

Question

2.)Light bulbs are normally distributed with an average lifetime of 1000 hours and a standard deviation of 250 hours. The probability that a light bulb picked at random will last between 1400 and 1500 hours is about:

3.) Bob 's daily commute time is randomly distributed with a minimum of 20 minutes, a maximum of 61 minutes, and the most common length is 30 minutes. What is the probability that his commute today took more than 35 minutes?

4.) If the mean time between unscheduled maintenance of LCD displays in a hospital's CT scan facility is 4,000 operating hours, what is the probability of unscheduled maintenance in exactly 5,000 hours?

5.) On average, 15 minutes elapse between discoveries of fraudulent corporate tax returns in a certain IRS office. What is the probability that more than 30 minutes will elapse before the next fraudulent corporate tax return is discovered?

6.) The most common size of trees in a grove is half the maximum of 20 feet. What is the typical amount that trees deviate from this most common size?

Explanation / Answer

2) X= 1400

z= (X-u)/sd

z= (1400-1000)/250= 1.6

P(X=1400) = P(z=1.6) = 0.9452

X= 1500

z= (1500-1000)/250= 2

P(X=1500)= P(z=2) = 0.9772

P(1400<X<1500) = P(X=1500) - P(X=1400)

= 0.9772 - 0.9452 = 0.032

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