Question 1201400
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I personally find it easier to count the numbers of ways of getting the desired results and then calculating the probability, rather than working with probabilities to do all the calculations.<br>
In counting the number of ways of getting the desired results, we use the inclusion-exclusion principle.  For example, in the first problem where the desired outcome is 2 kings or 2 face cards, we count the number of ways of getting 2 kings, add the number of ways of getting 2 black cards, and then subtract the number of ways we counted twice -- the ways that get 2 cards that are BOTH black AND kings.<br>
Then the other problem is worked in the same way.<br>
For both problems:  Number of ways of choosing 2 of the 52 cards: C(52,2) = 1326<br>
(1) P(both kings or both black)<br>
# of ways of getting 2 black cards: C(26,2) = 325<br>
# of ways of getting 2 kings: C(4,2) = 6<br>
# of ways of getting 2 black kings: C(2,2) = 1<br>
# of ways of getting 2 black cards or 2 kings: 325+6-1 = 330<br>
ANSWER: P(both kings or both black) = 330/1326 = 55/221<br>
(2) P(both face cards or both red)<br>
# of ways of getting 2 red cards: C(26,2) = 325<br>
# of ways of getting 2 face cards: C(12,2) = 66<br>
# of ways of getting 2 face cards both red: C(6,2) = 15<br>
# of ways of getting both face cards or both red: 325+66-15 = 376<br>
ANSWER: P(both face cards or both kings) = 376/1326 = 188/663<br>
Same answers as from the other tutor, by a different path.<br>
Neither path is better than the other; try both and find the one that "works" best for you.<br>