The amount of time a certain brand of light bulb lasts is normally distributed with a mean of 1200 hours and a standard deviation of 60 hours. What percentage light bulbs last less than 1160 hours, to the nearest tenth?
To find the percentage of light bulbs that last less than 1160 hours, we need to first calculate the z-score for 1160 hours using the z-score formula:
z = (X - μ) / σ
where X = 1160 hours, μ = 1200 hours, and σ = 60 hours.
z = (1160 - 1200) / 60
z = -40 / 60
z = -0.67
Next, we can use a standard normal distribution table or a calculator to find the percentage of values below z = -0.67.
From the standard normal distribution table, the percentage is approximately 25.5%.
Therefore, approximately 25.5% of light bulbs last less than 1160 hours.