SOLUTION: Consider a standard deck of playing cards (52 cards, no jokers). If you draw one card, what is the probability that the card is: a. a spade? b. a seven (7)? c. a seven (7) a

There are 13 spades out of 52 cards, so we put 13 over 52 and reduce:

There are 4 7's out of 52 cards, so we put 4 over 52 and reduce:

There is just one car that is both a 7 and a spade and
that is the 1 card the 7 of spades.  So we put 1 over 52:

Now we use the formula

P(A OR B) = P(A) + P(B) - P(A AND B)

P(7 OR Spade) = P(7) + P(Spade) - P(7 AND Spade)

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Edwin