If you know a card drawn is a Spade, what is the probability that the card is an Ace?

• A. 1/4
• B. 1/26
• C. 1/13
• D. 1/52

Answer: (C)

This is a conditional probability situation: once you know the card is a Spade, the sample space shrinks to the 13 spades. Among those, only one card is an Ace—the Ace of Spades. Therefore the chance the card is an Ace given it’s a Spade is 1 out of 13. The other options don’t fit the conditioning: 1/4 would be the chance of an Ace if suits didn’t matter, 1/26 isn’t tied to this restricted sample space, and 1/52 is the chance of drawing a specific card from the full deck without any condition.