Question 1080909
The short answer is that the numbers given determine the disk, not the fact that two disks are being chosen.  There are 6 possible numbers chosen, and half of them will produce a yellow.
The longer answer is that these are not independent events, which would allow one to multiply the probability.  The number and the disk are not independent; one determines the other.  There is a probability of getting a yellow of 4/10 with the first choice, and then it is 3/9.  But the choices are CONDITIONAL upon a certain number's being allowed.