Give the step-by-step reasoning process and then the final answer. Olga has an aquarium with fish in 5 different colors. There are 12 yellow ones, half as many blue ones, and twice as many green ones as yellow ones. How many fish does Olga have in her aquarium?
Olga has half as many blue fish as yellow ones, which means 12 * 0.5 = 6 blue fish. Green fish are twice as many as yellow ones, so in total there are 12 * 2 = 24 green fish. So all the fish sum up to 12 + 6 + 24 = 42.
The final answer: 42.