When a card is selected from a standard deck, what is the probability of getting a six and a spade?
#getting a 6 AND a spade"
The keyword here is "AND". The card that is chosen needs to be both a 6 AND a spade. There is only one card that satisfies both conditions, the 6 of spades.
There are 52 cards in a standard pack.
Compare this to the question: "getting a 6 OR a spade"
There are four 6s in a pack and 13 spades.
However, the 6 of spades is counted under both, so has been counted twice.