Posted by **HELPME** on Monday, December 19, 2011 at 9:34pm.

the life of electric bulbs has a normal distribution with a mean of 35 months and a standard deviation of 4 months. What should the warranty period be if the company that manufactures these bulbs does not want to replace more than 2% of the bulbs?

- statistics -
**PsyDAG**, Wednesday, December 21, 2011 at 1:47am
Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.02) and its Z score. Insert the value in the above equation and solve for the score. Remember that the Z score will be negative.

- statistics -
**Ashok Khile**, Saturday, January 21, 2012 at 2:36am
Here mean = 35

s.d.= 4

we have asked that

P(z)=0.98

see normal table

It is z=2.05

remember it is standard normal table value but we have to convert it for x variable for which mean is 35 and s.d. is 4.

do the inverse operation for which we convert x into z.

i.e.

x=mean+z*s.d.

x=35+2.05*4

x=47.3

rounding off it will be 48.

That is answer is 48.

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