Answer:
99.7%
Step-by-step explanation:
The empirical rule formula states that:
68% of data falls within 1 standard deviation from the mean - that means between μ - σ and μ + σ .
95% of data falls within 2 standard deviations from the mean - between μ – 2σ and μ + 2σ .
99.7% of data falls within 3 standard deviations from the mean - between μ - 3σ and μ + 3σ
Step 1
We have to find the number of standard deviations from the mean
μ = Mean = 1800 hours
σ = Standard deviation = 25 hours
For 1725 hours
μ - xσ =
1800 - 25x = 1725
25x = 1800 - 1725
25x = 75
x = 75/25
x = 3
For 1875 hours
1800 + 25x = 1875
25x = 1875 - 180
25x = 75
x = 75/25
x = 3
Step 2
From the above calculation, the bum of standard deviations from the mean is 3
Hence, the percentage of light bulbs last between 1725 hours and 1875 hours is 99.7%
