Thread: Standard Normal Distribution

Hello!

I'm not a math whiz. Wasn't in high school, and definitely not now. Especially since they have completely revamped the Math 33 curriculum -- this is stuff we didn't TOUCH in high school!

Anyways, probability is one of the worst. I've tried this over and over again and just cannot find the conclusion. If you could not only help me solve the problem, but walk me through step-by-step (treat me like an idiot, and maybe I"ll understand). Thank you SO much!!

Bean plants in a field have heights that are normally distributed, with a mean of 20.0 cm and a standard deviation of 3.5 cm. Find the proportion of plants that are between 15.8 cm and 24.2 cm tall.

So if z=x-u/o then:
z=15.8-20/3.5
z=-4.2/3.5
z=-1.2
which, according to the z-score table, equates to 0.0985

Alternatively:
z=24.2-20/3.5
z=4.2/3.5
z=1.2
which, according to the godly table, equates to 0.8849

Have I done this right so far? If so, this is where I get lost.... according to my textbook, I'm supposed to subtract 0.0985 from 0.8849, which is 0.7864.

The answer is 0.7699.

Where have I gone wrong? Thanks so much for helping!!

I figured out the problem.

I was reading the chart wrong. Boy, I feel dumb, but SO much better that I had the theory right!!

Back to work. Thanks anyways.