00:01
Hello students, to find the number of 9 digit numbers that can be obtained by using each of the digits 1, 2, 9, exactly 1 such that the number is bigger than 500000000, we need to consider the possible positions of the digit.
00:23
Since the number must be greater than 500000000, number is greater than 50 crore, the first digit must be either 6, 7, 8 or 9.
00:50
Let's consider, if the first digit is 6, then it can be also 5.
01:08
In this case, the digit 9 can occupy any of the remaining 8 positions excluding first position while the remaining 7 digits 1, 2, 3, 4, 5, 6, 7, 8 can be permitted among the remaining 7 positions.
01:23
Therefore, the total number of 9 digits is 8 into 7 factorial that is 40320.
01:34
Then first digit 7, similar the previous case, the digit 9 can occupy any remaining 8 positions while the remaining 7 digits can be permitted among the 7 positions.
01:50
So, 8 into 7 factorial that is 40320...
