Math  Standard Deviation
posted by GetYourLeash
A General Electric soft white 3way bulb has an average life of 1200 hours with a standard deviation of 50 hours. Find the probability that the life of one of these bulbs will be between 1150 and 1300 hours.
You need to change the times to Zscores â€” scores given in terms of standard deviations.
Z = (X  µ)/SD, where X is the particular value, µ = the mean and SD is the standard deviation.
Once the Z scores are obtained, look it up in a table in the back of your statistics textbook called something like "areas under the normal distribution." Find the proportions between those Zscores and the mean for both values and add them together to get the probability that the life of the bulb will be between these two values.
Although I did not solve the problem completely for you, I did tell you the process for reaching a solution. This will mean that you will have to exert a little more effort, time and thinking, but I hope it will help you to learn more.
I hope this helps. Thanks for asking.
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