Homework Help: maths

Posted by harish on Wednesday, February 13, 2013 at 7:22am.

The lifetime in hours of a certain make of batteries follows a normal distribution with mean 160 and standard deviation 30.
Calculate the interval, symmetrical about the mean within which 75% of the battery lifetimes lie.

maths - Reiny, Wednesday, February 13, 2013 at 10:24am
The following applet takes the place of your tables or charts traditionally used for this kind of work
http://davidmlane.com/normal.html

click on : value from an area
enter 0.75 in "area"
enter 160 in "mean"
enter 30 in "SD"

under "results" click "between"
click on "recalculate" to get

125.5 to 194.5

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