The life expectancy of a typical lightbulb is normally distributed with a mean of 2,000 hours and a standard deviation of 27 hours. What is the probability that a lightbulb will last between 1,975 and 2,050 hours?

Question

amistre64 · Answer

ti83 or table ?

amistre64 · Answer

if you have to table it, then find the z score of each value.  The zscore is the number of times the standard deviation fits into the distance between the mean and a stated value.$$z=\frac{x-mean}{sd}$$

amistre64 · Answer

if you can use a ti83 or stats calculator, find the normalcdf function;  for a ti83 you hit 2nd, VARS, and its the one that says normalcdf

then fill in the parameters given:  normalcdf(low, high, mean, sd)