1. Two companies, A and B, drill wells in a rural area. Company A charges a flat fee of $3500 to drill a well regardless of its depth. Company B charges $1000 plus $12 per foot to drill a well. The depths of wells drilled in this area have a normal distribution with a mean of 250 feet and a standard deviation of 40 feet.
Find the mean amount charged by Company B to drill a wall.
2. Jenn Bard, who lives in San Francisco Bay area, commutes by car from home to work. She has found out that it takes her an average of 28 minutes for this commute in the morning. However, due to the variability in the traffic situation every morning, the standard deviation of these commutes is 5 minutes. Suppose the population of her morning commute times has a normal distribution with a mean of 28 minutes and a standard deviation of 5 minutes. Jenn has to be at work by 8:30AM every morning. By what time must she leave home in the morning so that she is late for work at most 1% of the time?
Two statistic question (About mean standard deviation)?
2010-07-03 8:25 am
回答 (3)
2010-07-03 8:46 am
✔ 最佳答案
1. Am I missing something here, or is it this simple? The amount charged by Company B (that's the name of a theatre company in Sydney!!) is $(1000 + 12x) for a well of depth x ft.Mean charge = $(1000 + 12*mean of x)
.................. = $(1000 + 12*250)
.................. = $ 4000
2. Look at the normal distribution table (I'm using the one at http://www.math.unb.ca/~knight/utility/NormTble.htm) to see what standard score has only 1% of the distribution above it, i.e. the standard score that corresponds to 0.9900 in the table.
2.32 corresponds to 0.9898, and 2.33 corresponds to 0.9901, so I estimate 2.326 or 2.327 is the score we want. But the third figure probably doesn't matter.
2.326 standard deviations is
2.326*5 minutes
= 11.63 minutes
Let's work to the nearest minute and call that 12 minutes.
So the journey will take her more than 28+12 minutes only 1% of the time. That means she should leave 40 minutes before 8:30 a.m., i.e. at 7:50 a.m.
2016-03-03 6:51 pm
(91-73)/8=2.25 convert z score to a probability using the chart in your book z=2.25 (89-73)/8=2 (65-73)/8=-1 convert the 2 z scores to probabilities and subtract P(z=2) - P(z=-1) = answer
2015-10-28 1:44 pm
the first question is
a. What is the probability that Company B would charge more than Company A to drill a well?
a. What is the probability that Company B would charge more than Company A to drill a well?
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