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)

Results 1 to 9 of 9

- Jun 1st 2008, 05:15 AM #1

- Joined
- May 2008
- Posts
- 31

- Jun 1st 2008, 05:19 AM #2

- Jun 1st 2008, 05:43 AM #3

- Joined
- May 2008
- Posts
- 31

- Jun 1st 2008, 05:46 AM #4

- Joined
- May 2008
- Posts
- 31

- Jun 1st 2008, 05:49 AM #5

- Jun 1st 2008, 06:01 AM #6

- Joined
- May 2008
- Posts
- 31

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, 06:05 AM #7

- Jun 1st 2008, 06:30 AM #8

- Joined
- May 2008
- Posts
- 31

- Jun 1st 2008, 01:42 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