Question 370437: Life of Light Bulbs A certain type of light bulb has an average
life of 500 hours, with a standard deviation of 100 hours. The
length of life of the bulb can be closely approximated by a normal
curve. An amusement park buys and installs 10,000 such
bulbs. Find the total number that can be expected to last for
each period of time.
Q:Find the shortest and longest lengths of life for the middle
80% of the bulbs.
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! Life of Light Bulbs A certain type of light bulb has an average
life of 500 hours, with a standard deviation of 100 hours. The
length of life of the bulb can be closely approximated by a normal
curve. An amusement park buys and installs 10,000 such
bulbs. Find the total number that can be expected to last for
each period of time.
Q:Find the shortest and longest lengths of life for the middle
80% of the bulbs.
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The middle 80% has a left tail of 10% and a right tail of 10%
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The z-value with a left tail of 10% = -1.2816
The z-value with a right tail of 10% = 1.2816
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Life cutoff for the lowest 10% = -1.2816*100+500 = 372 hrs.
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Life cutoff for the top 10% = 1.2816*100+500 = 628 hrs
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Cheers,
Stan H.
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