Asked by Kruti
The life time of a certain kind of batteries has a mean life of 400 hours and standard deviation as 45 hours. Assuming the distribution of life to be normal, find i) the percentage of batteries with a life time of atleast 470 hours. Ii) Out of 10000 batteries how many batteries do you expect to have life between 385 and 415 hours.
Answers
Answered by
Reiny
This page will replace any tables or charts in the back of texts or handouts you might have been given
http://davidmlane.com/hyperstat/z_table.html
enter:
mean -- 400
SD -- 45
click on "above" and enter 470
prob is .0599 ---> 5.99%
ii) click on "between" and enter the values
multiply the prob by 10000
The beauty of this page is that you don't have to find z-scores first.
If your course requires you to work with z-scores, then find those scores for all your numbers, and set the mean to 0 and the SD to 1, then enter the data as z-scores.
You will get the same results.
http://davidmlane.com/hyperstat/z_table.html
enter:
mean -- 400
SD -- 45
click on "above" and enter 470
prob is .0599 ---> 5.99%
ii) click on "between" and enter the values
multiply the prob by 10000
The beauty of this page is that you don't have to find z-scores first.
If your course requires you to work with z-scores, then find those scores for all your numbers, and set the mean to 0 and the SD to 1, then enter the data as z-scores.
You will get the same results.
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