the life expectancy of a typical light bulb is normally distributed with a mean of 2000 hours and a standard deviaton of 27 hours. what is the probability that a lightbulb will last between 1975 and 2050 hours?
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convert 1975 and 2050 to z-scores using the formula z-score = (given number - mean)/standard deviation
then use a z-table or a calculator (normalcdf(z-score1,z-score2) to find the probability
hm, not quite, can you tell me where you got your answer?
I'm a little confused on how to do this all. The two answers I got were -.925925926 and 1.851851852
your numbers are right, you're just not done yet
1. find the probability that corresponds to -.925925926 using the z-table
2. find the probability that corresponds to 1.851851852 using the z-table
take the result from part 2 and subtract the result from part 1
I got .925925926
uh, not quite
use the z-table to find the probability that corresponds to -.925925926
actually, do you have a graphing calculator with you?
No I don't
alright, so for the z-score -.925925926 we're going to round to -0.93, and use this z-table to find the probability
look at the left column and find the row -0.9, then go across to the column 0.03 and tell me what number is in the box
.1762 so it's the first answer. Thank you :)
It was C.
ahh sorry for the late reply
you're supposed to do the same thing we just did for 1.851851852 and subtract the two values