Normal distribution problem. Please Help

[godales77]

I have a few homework questions like this, and I have no idea how to start it or finish it. Can someone please help and show the work on how to complete this problem? That would be great. Thanks.

The shelf life of a battery produced by one major company is known to be normally distributed, with a mean life of 4.4 years and a standard deviation of 1.3 years. What is the probability (as a percent to two decimal places,e.e. 95.44) that a randomly choosen battery will

(a) last fewer than 3.1 years?
Answer:

(b) last between 1.8 and 7 years?
Answer:

(c) last more than 0.5 years?
Answer:

 

[wjm11]

The shelf life of a battery produced by one major company is known to be normally distributed, with a mean life of 4.4 years and a standard deviation of 1.3 years. What is the probability (as a percent to two decimal places,e.e. 95.44) that a randomly choosen battery will

(a) last fewer than 3.1 years?
Answer:

(b) last between 1.8 and 7 years?
Answer:

(c) last more than 0.5 years?

Calculate a z score for each of the four times listed in the problems. A z score is just the number of standard deviations away from the mean. Here are a couple of sites if you need more info:

http://www.fourmilab.ch/rpkp/experiment ... zCalc.html
http://www.animatedsoftware.com/statglos/sgzscore.htm

After finding the z score, look at Table A (Standard Normal Table) in your stats book to find out what probabilities lie on each side of that score. More info:

http://www.statsoft.com/textbook/distribution-tables/#z
http://www.mathnstuff.com/math/spoken/h ... /other.htm