In a bag of marbles, you have three green, two yellow, six blue, and nine red marbles. what is the probability of picking a blue marble from the bag?

I had problems like these how I figure them out is

I add all the marble i have So 3 green marbles + 2 yellow marbles + 6 Blue marbles + 9 red marbles = 20 marble altogether

The probability of picking a blue marble out the bag is 

Because there is 20 marble and 20 of those marbles are blue

Just like the probability of picking a red marble is 

The probability of picking a green marble is 

And the probability of picking a yellow marble is 

So your answer for the probability of picking a blue marble from the bag is