statistics research
posted by Lauren .
What proportion of adults use between 15 and 23 gallons of gas per week if it is normally distributed with a mean of 16 gallons and a standard deviation of 5 gallons?

See your other post.

Use zscores. You need to find two zscores, then find the proportion between the two using a ztable.
Formula:
z = (x  mean)/sd
For the first z:
x = 15
mean = 16
sd = 5
For the second z:
x = 23
mean = 16
sd = 5
Plug the values into the formula and calculate to find the two zscores. Then check a ztable for the proportion between the two.
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