The life expectancy of a typical lightbulb is normally distributed with a mean of 4,000 hours and a standard deviation of 42 hours. What is the probability that a lightbulb will last between 3,875 and 4,055 hours?

0.8835

0.7825

0.9133

0.9035

Question

The life expectancy of a typical lightbulb is normally distributed with a mean of 4,000 hours and a standard deviation of 42 hours. What is the probability that a lightbulb will last between 3,875 and 4,055 hours?

 0.8835

 0.7825

 0.9133

 0.9035

mallorysipp234 · Answer

@4075754545 ???

mallorysipp234 · Answer

@IAmSinged ? (:

mallorysipp234 · Answer

@agent0smith @AccessDenied @ganeshie8 @Hero @iambatman @iPwnBunnies @jim_thompson5910

anonymous · Answer

You convert the range of values into a range of z scores.
z = value - mean/ Standard Deviation

3875 => z of around - 2.975
4055 => z of around 1.310

Then you consult a table of z values and do the math (a graphing calculator should be able to do this also, but I used a table when I had stats).

mallorysipp234 · Answer

@IAmSinged im confused? what do i do with these?

mallorysipp234 · Answer

@jim_thompson5910 @mathstudent55

mallorysipp234 · Answer

@Reaper534 @Hero  someone please help.