﻿pnorm(54, mean=51, sd=25) - pnorm(52, mean=51, sd=25)  # (1)
pnorm(52, mean=51, sd=25) - pnorm(49, mean=51, sd=25)  # (2)
1.0 - pnorm(61, mean=51, sd=25)  # (3)
pnorm(0, mean=51, sd=25)  # 試験の点数が負になる確率