# Math Help - 52 card deck (a red or a 7)

1. ## 52 card deck (a red or a 7)

Hi, here is my question. From a 52 card deck, what is the probability that I will pull a red or a 7. I got 1/26. Is this right.?

2. Originally Posted by Hunt67
Hi, here is my question. From a 52 card deck, what is the probability that I will pull a red or a 7. I got 1/26. Is this right.?
how did you get that?

method 1: count how many choices you have:

there are 26 red cards, including 2 7s, besides that, there are two 7s, so that we have 28 choices in all out of 52. thus the probability is 28/52 = 7/13

method 2: use the formula

for two events $A$ and $B$

$P(A \cup B) = P(A) + P(B) - P(A \cap B)$

here that translates to $P( \text{red or 7}) = P(\text{red}) + P(7) - P( \text{red and 7}) = \frac {26}{52} + \frac 4{52} - \frac 2{52} = \frac 7{13}$