00:01
Okay, so we're told that on this test the scores range from 0 to 1 ,600.
00:07
Okay, we're told to use the range rule of thumb to make a rough estimate of the steering deviation.
00:18
And the range rule of thumb says that if you take the range and you divide it by 4, then that should give you a pretty good estimate of the staring deviation.
00:31
So taking 1600 divided by 4 because 1600 minus 0 would be the range, that gives me 400 for my estimate.
00:44
So now i am going to use that estimated seren deviation to determine the sample size n for a 95 % confidence interval with a margin of error of 100 points.
01:03
To calculate a confidence interval, it would be x bar plus or minus z star times sigma over the square root of n.
01:11
And that z time z star times sigma over the square root of end, that would be your margin of error.
01:18
So what we need to do here is just set that margin of error equal to 100.
01:26
Z star for 95 % confidence is always going to be 1 .96.
01:31
That's how far you have to go out on the standard normal curve to get 95 % of the data.
01:38
Times sigma, which i said was about 400 over the square root of n.
01:43
I don't know what that is yet, but that's what i'm solving for...