createCanvas(400, 400);

}

​

function draw() {

  background(0);

  stroke(255);

  line(200,200,mouseX,mouseY);

  var x = ave(200,mouseX);

  var y = ave(200,mouseY);

  fill(255,0,0);

  ellipse(x,y,30,30);

  //challenge: use the ave function again to make

  //a green dot half way between the center and the

  //red dot

  var x2 = ave(200,x)

  var y2 =ave(200,y)

  fill(0,255,0);

  ellipse(x2,y2,30,30);

}

function ave(num1, num2){

  return (num1+num2)/2

}

​