(hard.) in a certain psychology experiment, each subject is presented with three ordinary playing cards, face down. the subject takes one of these cards. the subject also takes one card at random from a separate, full deck of playing cards. if the two cards are from the same suit, the subject wins a prize. what is the chance of winning

The answer to this question would be 1/4
To answer this question you need to know what the same suit means and how many cards in a deck is. In the standard card, there are 52 cards in a deck. The deck also compromised of 4 suit which was clubs (♣),  hearts (♥), spades (♠) and diamonds (♦), Each suit has the same number ratio from those 52 cards, which mean 13 cards for each suit.
In this test, the subject takes one of three cards first. There is no information about this card, so we can assume that it is completely random and having one of the 4 available suits. After that, the subject takes a card from the separate full deck.
Then the chance to get the same suit would be 13/52= 1/4 chance