Value Watt lightbulbs have an average lifetime of 740 hr of use before burning out, with a standard deviation of 80 hr, according to the quality control department. Assume these times are normally distributed.

What percent of bulbs will burn out before being used 660 hr?

Question

Value Watt lightbulbs have an average lifetime of 740 hr of use before burning out, with a standard deviation of 80 hr, according to the quality control department. Assume these times are normally distributed.

What percent of bulbs will burn out before being used 660 hr?

anonymous · Answer

A is 31.1%
B is 13.5%
C is 50%
D is 47.5%
E is 15.9%

directrix · Answer

Use the attached formula to find the z-score that goes with 660. Once you find that, post what you got for z here. We will then have to find the appropriate area under the standard normal curve that gives the percentage of bulbs that will burn out before 660 hours of use.

directrix · Answer

@heartnc