The numbers 1,2,3,4 and 5 are written on slips of paper, and 2 slips are drawn at random one at a time without replacement. Find the probability the first number is 2 or the sum is 6

Answer 1

P(A or B) = P(A) + P(B) - P(A and B)

P(A) is 1/5

P(B): there are 5 ways to get sum 6 -- 1+5, 2+4, 3+3, 4+2 and 5+1... and there are 25 ways to draw the 2 numbers...P(B) = 5/25 = 1/5

P(A and B)...there is only one way to get both: 2+4...again out of 25 ways

P(A or B) = 1/5 +1/5 - 1/5 = 1/5

P.S.

To see the probability for the sum, make a 5 * 5 table and at the intersection squares, write the sum...you will see that there are 25 possible outcomes, only 5 of which are sum 6.