Here is what we know...
There is a total of 15 cards
Adding brown and yellow cards together is 12/15 cards
The probability of picking a brown or yellow card is 12/15 since there are 12 yellow and brown cards and a total of 15 cards. You still need to simplify this though.
12 and 15 can both be divided by 3 (12/15)
12 divided by 3 = 4
15 divided by 3 = 5
This simplifies into 4/5
The probability that a yellow or brown card is chosen from the box is 4/5
