There are 5 yellow marbles and 12 blue marbles in a bag. You randomly choose one of the marbles. What is the probability of choosing a yellow marble? Write your answer as a fraction in simplest form.

Megan and desmond each add the same amount of water to their aquarium megan makes 5 ml of chemical solution with every gallon of water for her aquarium desmond mixed 8 ml of chemical solution for every 2 gallon of the water for his aquarium.