The total number of possible cases can be given by selecting any one digit out of the ten digits which has to come thrice and selecting the remaining digits.So, the total cases = Cases when one of 9,8,7 come thrice + Cases when 9,8,7 come once =   3C1 * 7C3 * 5! / 2! + 7C1 * 6C2 * 5! / 3! = 3 * 35 * 60 + 140 * 15 = 140 * 60 = 8400Now, the favorable cases = 7C1 * 6C2 * 5! / 3! = 140 * 15 = 2100Hence, the probability = 1/4.

probability qa sectional 3 Screenshot 2024-11-04 050821.png 102.95 KB

probability qa sectional 3 Screenshot 2024-11-04 050821.png 102.95 KB