a) Profits (denoted asX) 100 normally distributed mean value of 1.5 mi and a (s.d.) of 120,000.

Calculate P (X< $1 million)

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- Jun 1st 2008, 04:15 AM #1

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- Jun 1st 2008, 04:19 AM #2

- Jun 1st 2008, 04:43 AM #3

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Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000.

so i do the same steps as the rest?

so here i would use T as the random sample of 10 is under 30, 30 and over i use z system and for T 29 and less . is that correct?

- Jun 1st 2008, 05:05 AM #7

- Jun 1st 2008, 05:30 AM #8

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- Jun 1st 2008, 12:42 PM #9
Use the t-distribution because the population sd is unknown. Although n is small (n < 30), from your previous question it's known that the data comes from a normal population so using the t-distribution is OK.

As for the confidence interval, you will find the necessary formulae at this thread: http://www.mathhelpforum.com/math-he...intervals.html

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