10 test paper, 4 papers are difficult to draw, 3 people draw lots, A draws first, B draws second, C finally, how to prove that the probability of three people drawing difficult papers is equal?

The probability that A draws a lot of difficult signatures =4/ 10=0.4.

B The probability of drawing lots is 4/10 * 3/9+6/10 * 4/9 =12/90+24/90 = 36/90 = 0.4.

The probability that C is difficult to draw is 4/10 * 3/9 * 2/8+4/10 * 6/9 * 3/10 * 4/9 * 3/8+6/1.

=24/720+72/720+72/720+ 120/720=288/720

=0.4

The calculation process is like this. The more people draw lots, the more difficult it is to calculate the probability behind, because it is necessary to distinguish that no one in front can draw lots, but everyone draws lots with equal probability, regardless of the lottery order.