Question 765442
A card is drawn from a well-shuffed deck of 52 cards. Find the probability that the card is a black card or a five. 

No. of cards in deck = 52
No. of black cards = 26 (Two suits of spades, clubs)
So, Probability of drawing a black card = 26/52 = 1/2

No. of 5's = 4 (one 5 in each suit)
So, Probability of drawing a 5 = 4/52 = 1/13

But here's the catch - there are 2 cards which are both black and 5 (5 of 
spades, and 5 of clubs). These 2 would get counted twice in both the above sets. We need to subtract that.

No. of cards which are both black and 5 = 2 (5 of spades, 5 of clubs)
Probability of drawing a black 5 = 2/52 = 1/26

Hence, no of possibilities of getting a black OR 5 =

Probability of drawing a black +
probability of drawing a five -
probability of drawing a black 5 

= 1/2 + 1/13 - 1/26 = (13 + 2 - 1)/26 = 14/26 = 7/13

Hope you got it :)