10, the probability that 4 people are difficult to sign, 3 people draw lots for oral test, A draws first, B draws later, and C draws (1)A, B and C are difficult to sign.

C(4，3)/ C( 10，3) = 4/ 120 = 1/30

The probability that a is difficult to sign is:

4/ 10=2/5

The probability of B drawing lots is the same as that of A, and so is C. The drawing lots have nothing to do with the order.