Wednesday

April 23, 2014

April 23, 2014

Posted by **alice** on Wednesday, December 5, 2012 at 1:36pm.

My guess was: percentile = 9000 hours/400 lightbulbs = 22.5, but I'm not sure if I'm solving this right

- Math -
**alice**, Wednesday, December 5, 2012 at 1:50pmThis is from the actual problem - A consumer product testing lab tested 400 13-watt compact

fluorescent light bulbs by turning them all on at once, leaving them

on until they burned out, and recording the time-to-failure of each

bulb. The test revealed a symmetric and mound-shaped

distribution of times-to-failure with mean 7800 hours and standard

deviation 1200 hours. The number of lightbulbs that lasted between 5400 and 9000 hours were about 326 lightbulbs.

**Related Questions**

Math - For a normally distributed distribution of variable x, where the mean is ...

percentile rank - i would like to able to find the percentile rank of a z score ...

statistics - The following frequency distribution presents a set of exam scores ...

Math - Rank the following data in increasing order and find the positions and ...

Statistics: Percentile Rank - A survey of college students was conducted during ...

Math - Can someone please help me with these three question? I having a very ...

math - If a student's percentile rank in a class of 400 students is 87, find the...

Math - If a student's percentile rank in a class of 400 students is 87, how do ...

algeba - if a student's rank in a class of 400 students is 44 find the student's...

Stats - If a student's rank in a class of 300 students is 111, find the student'...