Answer:
mean = 85, standard deviation = 3.5
Step-by-step explanation:
The empirical rule states that for a normal distribution, 68% of the data falls within one standard deviation of the mean, 95% falls within two standard deviation of the mean and 99.7% falls within three standard deviation of the mean.
From the diagram since the shaded are is approximately 95% of the data. Hence 95% falls within two standard deviations of the mean.
σ = standard deviation, μ = mean
Hence; μ ± 2σ = (78, 92)
μ - 2σ = 78 (1);
μ + 2σ = 92 (2)
Adding equation 1 and 2, gives 2μ = 170
μ = 85
μ - 2σ = 78
85- 2σ = 78
2σ = 7
σ = 3.5
