Use the hold functionality and plot them as you will do normally for a plot.
example:
x = linspace(0,3*pi,200);
rng(0,'twister');
y = cos(x)+ rand(1,200);
figure
scatter(x,y)
hold on
scatter(x,2*y,'r')
x(length(x)/2:end)=[];
y(length(y)/2:end)=[];
scatter(x,y/2,'g')
