A company installs 5000 light bulbs, each with an average life of 500 hours, standard deviation of 100 hours, and distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time. Less than 690 hours.
A. 97.06%
B. 47.14%
C. 97.1%
D. 97.2%

Question

A company installs 5000 light bulbs, each with an average life of 500 hours, standard deviation of 100 hours, and distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time. Less than 690 hours.
A. 97.06% 	
B. 47.14% 	
C. 97.1% 	
D. 97.2%

amistre64 · Answer

it looks like we need to know the ztable value for 1.9 standard deviations

amistre64 · Answer

or, do you have a ti83 or similar stat calculator handy?

anonymous · Answer

yea i have a ti-84 plus.. please help me

amistre64 · Answer

with the ti-84, you should have a 2nd button; we want to get into the Distr menu this way:

2nd ->  VARS  and we are in

we want the cumulative function for a normal distribution; choose normalCDF()

this function takes 4 arguments,  low, high, mean, sd

so you would enter all that info into the function like this

normalCDF(-9999,690,500,100)

the -9999 is just an arbitraryly low value since we cant insert -infinity into the thing

the result is a decimal value that tells us the percentage of bulbs that are last the time period of 690 hours or less ....