How many different four digit numbers can be made up of 4, 0, 9 and 1

If the 100 digit number of a three digit number is a, the 10 digit number is B, and the one digit number is C, the position of the 10 digit number of the three digit number and the 100 digit number can be obtained
If there is a new three digit number, the difference between the two three digits is not only a multiple of 3, but also a multiple of 5. Why
It's tonight

The first three digit can be expressed as: 100A + 10B + C, the second three digit is: 100b + 10A + C, then the difference between the two is expressed as: (100a + 10B + C) - (100b + 10A + C) = 90 (a-b). Because 90 is a multiple of 15, it is a multiple of 3 and a multiple of 5

A 3-digit number with a ten digit number of 0 is equal to m times of the sum of each number. By exchanging the positions of its hundred and single digits, the 3-digit number is n times of the sum of each number, n
Find n

You can set one digit as X and one hundred digit as y
Then, we get: three digit = 100y + x = m (x + y)
After exchanging its 100 digit and one digit positions, we get the following results:
New three digit = 100x + y = n (x + y)
Solve the equation. N = 101-m

If a ten digit number is three digits of 0, it is equal to 67 times of the sum of its digits; if the new three digit number is m times of the sum of its digits, then M =

100x+y=67(x+y)
100y+x=m(x+y)
Then x = 2Y
m=34
Let a hundred digit be x and a single digit be y

How many different four digit numbers can be made up of 4, 0, 9 and 1