A psychologist has been studying eye fatigue using a particular measure,
which she administers to students after they have worked for 1 hour writing on
a computer. On this measure, she has found that the distribution follows a
normal curve. The test of eye fatigue has a mean of 15 and a standard deviation
of 5. Using a normal curve table, what score on the eye fatigue measure would a
person need to have to be in the top 40%?
On the table you have to find what z-score has a 0.60 area meaning its in the top 40% because 60% of the curve is below it. This is going to give a z-score of about .26 (the area for this is 0.6026). The formula for z-score is (value-mean)/standard deviation. z=(v-m)/s We can rearrange this to zs=v-m then zs+m = v
Plugging in values we get zs+m=v, (0.26)(5)+15=16.3
If you want want a calculator would tell you I can redo the math because it will have a more accurate z-score.
Don't be afraid to ask me any more questions. Please ask me for clarification before you withdraw.