15 phones have just been received at an authorized service center. 5 are cellular, 5 are cordless, and 5 are corded. Suppose service tickets have been issued for these phones allocating all numbers 1 through 15 indicating the order in which they will be serviced. Find the probabilities that:
after having repaired 10 phones, there are phones of exactly two of the three types remaining to be serviced.
I computed the answer to be [3 x [(10 C 5) - 2]]/(15 C 10)
Is this correct