Instead of tables I use this applet
http://davidmlane.com/hyperstat/z_table.html
When you say 25 percentile, doesn't that mean that 25% of the date is below?
Your answer of 271 is above the mean, therefore more than the 50% percentile.
using the second part , entering 365 for mean, and 10 DV, I entered .25 for "shaded area" and clicked on below to get 358.25
similarly for your second, doesn't top 10% mean that 90% are below??
so enter mean=36 sd=10 .9 for shade and click below to get 48.8
(how could your score of 28.15, which is well below the average of 36 put somebody in the top 10% ?)
Section 5.3: Normal Distributions: Finding Values
Answer the questions about the specified normal distribution.
Q1: The lifetime of ZZZ batteries are normally distributed with a mean of 265 hours and a standard deviation ó of 10 hours. Find the number of hours that represent the the 25th percentile.
A1:
x = µ + zó
= 265 + -0.608 (10)
= 271.08
Q2: Scores on an English placement test are normally distributed with a mean of 36 and standard deviation ó of 6.5. Find the score that marks the top 10%.
Q2:
x = µ + zó
= 36 + -1.208 (6.5)
= 28.15
2 answers
A survey was conducted to measure the number of hours per week adults spend on home
computers. In the survey, the number of hours was normally distributed, with a mean of 8
hours and a standard deviation of 1 hour. A survey participant is randomly selected. Find
the probability that the hours spent on the home computer by the participant are between
5.5 and 9.5 hours per week.
computers. In the survey, the number of hours was normally distributed, with a mean of 8
hours and a standard deviation of 1 hour. A survey participant is randomly selected. Find
the probability that the hours spent on the home computer by the participant are between
5.5 and 9.5 hours per week.
1 answer