Hi.

There are 9 numbers divisible by 3:

3

6

9

12

15

18

21

24

27

(Because 27 : 3 = 9)

and there are 6 numbers divisible by 4:

4

8

12

16

20

24

(27 : 4 = 6,...)

The probability of picking a particular card (e. g. the card has the number 5 on it) is 1/27. This is obvious, is it?

There are 6+9 = 15 of 27 numbers divisible by 3 or 4, so the asked probabilty is 15/27

: downthesun01 is right, I counted some numbers twiceEdit