If you allow the first digit to be zero, then you can form (5 x 4 x 3 x 2 x 1) = 120 numbers.
If the first digit can't be zero, then you can only form (4 x 4 x 3 x 2 x 1) = 96 numbers.
# 230 # 203 # 320 # 302
With repetition, 94 = 6561. Without repetition, 9*8*7*6 = 3024.
9 odd numbers less than 100 can be formed. They are: 3,5,7,35,37,53,57,73 and 75.
There are 2000 such numbers.
There are 4 ways to chose the first digit. Then because there is to be no repetition, there are 3 ways to choose the second. This means that there are 4 x 3 ways of setting down the first two digits 12 _ _ 13 _ _ 14 _ _ 21 _ _ 23 _ _ 24 _ _ 31 _ _ 32 _ _ 34 _ _ 41 _ _ 42 _ _ 43 _ _ .... now you can take it from there.
15 of them.
I take it that you want to make three digits numbers with 8,7,3, and 6 without repetition. The first digit cane be selected from among 4 digits, the second from 3 digits, the third digit from 2, hence the number of three digit numbers that can be formed without repetition is 4 x 3 x 2 = 24
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
Six (6)
3*2*1 = 6 of them.
9*8*7 = 504 of them.
64 if repetition is allowed.24 if repetition is not allowed.
# 230 # 203 # 320 # 302
1
If repetition of digits isn't allowed, then no13-digit sequencescan be formed from only 5 digits.
125
There are 4*4*3*2*1 = 96 such numbers.