Asked by Ashley

the average student sends about 200 text messages a day with the standard deviation of 25 texts.(show graph)

a.what is the probability that a student sends more than 250 messsages a day?
b.what is the probability that student sends less than 150 text messages a day?
c.what is the probability that a student sends between 180 and 240?
d.what is the probability that a student ssends exactly 250 text messages a day?
e.find the cutoff number fot the middle 60% of text messages sent per day?
f. find the top 25% of the number of text messages sent per day?
g.find the bottom 10% of text messages sent per day
Answered by PsyDAG
Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions for the Z scores.

For e, f, g, find the proportion first and use the Z score in the above equation.

Here is the graph:

http://en.wikipedia.org/wiki/Standard_deviation
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