There are only 7 blue pens,4 green pens and 6 red pens in a box. One pen is taken at random from the box.
Write down the probability that the pen is blue

The general form of the quetion of a circle is ax^2+by^2+cx+dy+e=0 where a=b=0 if the circle has a radius of three units and the center lies on the y axis which set of values of a, b, c, d, and e might correspond to the circle