To find the percentage of light bulbs that last more than 1680 hours, we need to find the z-score for 1680 hours and then find the percentage of data that falls above this z-score in a standard normal distribution table.
First, calculate the z-score:
Z = (X - μ) / σ
where X = 1680 hours, μ = 1700 hours, and σ = 40 hours
Z = (1680 - 1700) / 40
Z = -0.5
Next, find the percentage of data that falls above a z-score of -0.5 in a standard normal distribution table. Looking up the z-score in the table or using a calculator, we find that the percentage is 69.15%.
Therefore, approximately 69.15% of light bulbs last more than 1680 hours.
The amount of time a certain brand of light bulb lasts is normally distributed with a mean of 1700 hours and a standard deviation of 40 hours. What percentage light bulbs last more than 1680 hours, to the nearest tenth?
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