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\[ s^2 = \frac{1}{n-1} \ sum_{i=1}^{n} (X_i - \bar{x})^2 \]

iphoneUsage = data.frame( hours = rnorm(200, mean = 4.5, sd = 1.2))

sampleMean = mean(iphoneUsage$hours)

ggplot(iphoneUsage, aes(x = hours)) +
  geom_histogram(binwidth = 0.5,
          fill = "pink", color = "white", alpha = 0.7) + 
  labs( title = "Daily Iphone Screen Time", 
        x = "Hours Per Day", 
        y = "Number of Users") + 
  theme_minimal()