A box is filled with 5 red cards, 3 brown cards, and 4 green cards. A card is chosen at random from the box. What is the probability that it is a red or a green card?

Question

A box is filled with 5 red cards,  3 brown cards, and  4 green cards. A card is chosen at random from the box. What is the probability that it is a red or a green card?

amistre64 · Answer

how many red or green cards are there? =s
how many cards there there altogether? =n

use the basic rule the defines a probability as the number of events defined to happen, divided by the number of total events that could happen:$$P(X)=\frac sn$$