z30 <- (30 - 29.11) / 0.93; z30 # z-score for 30 min
z31 <- (31 - 29.11) / 0.93; z31 # z-score for 31 min
xpnorm(c(30, 31), 29.11, 0.93) # original normal distribution proportion between 30 and 31 min
xpnorm(c(z30, z31)) # standardized distribution proportion between 30 and 31 min
pnorm(z31) - pnorm(z30)
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