My Math Forum probablity in interval

 May 13th, 2012, 05:46 AM #1 Newbie   Joined: May 2011 Posts: 28 Thanks: 0 probablity in interval Hello, Could you help me with this: Four speedmeters measured these values: 191, 199, 196 and 194 km/h. Standart deviation is 2 km/h (we can consider normal distribution). There are no errors in the measurements. What is the probability that speed is in interval (193, 195) ? thanks
 May 13th, 2012, 09:16 AM #2 Member   Joined: Nov 2009 Posts: 90 Thanks: 0 Re: probablity in interval Hello token22, According to this video lecture, the standard error of the mean (SEM) is 1/2. http://www.youtube.com/watch?v=J1twbrHel3o So 193 is 4 SEM from the sample mean. Using another video lecture as guidance, this should make your probability close to (just a tiny bit smaller than) 50%. http://www.youtube.com/watch?v=bekNKJoxYbQ Now you're gonna have to confirm this, because I'm quite sloppy. Let us know how it goes.
 May 13th, 2012, 12:21 PM #3 Newbie   Joined: May 2011 Posts: 28 Thanks: 0 Re: probablity in interval Oh i forgot to those youtube demonstration videos, anyway I got 0,4772 by video you sent, so it could be fine.
 May 13th, 2012, 01:52 PM #4 Member   Joined: Nov 2009 Posts: 90 Thanks: 0 Re: probablity in interval Oh, that's right. SEM = s/(n^.5) = 2/(4^.5) = 1 So 0.4772 is right. Yeah, Mr Khan is awesome!

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