Posted by **Lauren** on Friday, February 24, 2012 at 3:44pm.

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?

- statistics research -
**MathGuru**, Friday, February 24, 2012 at 7:01pm
See your other post.

- statistics research -
**MathGuru**, Friday, February 24, 2012 at 7:05pm
Use z-scores. You need to find two z-scores, then find the proportion between the two using a z-table.

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 z-scores. Then check a z-table for the proportion between the two.

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