qnorm(.8, 100, 15)

abline(v=qnorm(.8, 100, 15), lty=4 )

sr <- 100; odch <- 15
x <- seq(-4, 4,length=1000) * odch + sr
p <- dnorm(x, sr, odch)
plot(x,p, type="l", lwd=2)
pnorm(80, 100, 15)
abline(v=80, lty=2)
plot(x,p, type="l", lwd=2)
qnorm(.8, 100, 15)
abline(v=qnorm(.8, 100, 15), lty=4)
text(x=95, y=.01, labels="80%", cex=1.5)

x <- 0:200
p <- dnorm(x, 100, 15)
plot(x,p, type="l", lwd=2, xaxs="i", yaxs="i", bty="l")
abline(v=qnorm(.80, 100, 15), lty=4)
text(x=95, y=.01, labels="80%", cex=1.5)

v=qnorm(.8, 100, 15)
axis(1,at=v,v)