2 cards are drawn without replacement from an ordinary deck of 52 playing cards. What is the probability that both are spades if the first card drawn was a spade?

I think you subtract out the first spade making the probability 12/51 since you take off the first card already turned. Am I right? Do we put the probability in fractional format or percent?

Since there are only 12 spades left on the remaining 51 cards, 12/51 is correct.

I prefer to leave probabilities in fractional format because it is exact, while conversion to decimal produce an approximation most of the time.