the distribution of the scores on a standardized exam is approximately normal with mean 400 and standard deviation 35. Between what values do the middle 50 percent score lie?
2006-12-18 08:43:10 · 2 answers · asked by Eugene D 1 in Science & Mathematics ➔ Mathematics
Please don't blame me if I'm wrong. I am not a statistics expert at all, but I'm trying to re-learn and re-teach myself.
Looking at a "z-table", such as http://www.statsoft.com/textbook/sttable.html#z, it appears that 25% away from 0.0 (which is the mean) lies at between 0.6 and 0.7z, closer to 0.7.
Therefore, if I understand correctly, the 50% cutoff should be at about 0.7 times the standard deviation, or about 24.5.
So the middle 50% of scores should lie between 400 - 24.5 = 376.5 and 400 + 24.5 = 424.5.
2006-12-18 08:57:31 · answer #1 · answered by Jim Burnell 6 · 1⤊ 0⤋
400 - 0.6745*35 < X < 400 - 0.6745*35
376.3 < X < 423.6
2006-12-18 16:58:54 · answer #2 · answered by Helmut 7 · 1⤊ 0⤋