Find the index that represents a percentage of area

Hello,

I have a probability distribution with mean mu = 0 and a standard deviation s = 1.

I want to plot a vertical line that represents the 20% for example of the total area (as in the figure attached).

How I can do this?

Thanks

s = 1; mu = 0; xstart = -10; xend = 10; xstep = 0.1;
x_range = xstart:xstep:xend;
my_pdf = normpdf(x_range,mu,s);
figure
plot(x_range,my_pdf,'b');

Answer 1

[David Hill]

s = 1; mu = 0; xstart = -10; xend = 10; xstep = 0.1;
x_range = xstart:xstep:xend;
my_pdf = normpdf(x_range,mu,s);
figure
x=norminv(.2,mu,s);
y=0:.01:.4;
x=x*ones(size(y));
plot(x_range,my_pdf,'b',x,y,'r');

[Khoder Makkawi]

Thank you