Number of 7 digit combinations out of the 10 one-digit numbers = 120.
Using the digits of 1345678, there are 210 three digit numbers in which no digit is repeated.
There are 5 numbers which can make the 3 digit numbers in this example. Therefore each digit in the 3 digit number has 5 choices of which number can be placed there. Therefore number of 3 digit numbers = 5 x 5 x 5 = 125
You have 4 options for the first digit, 3 for the second, 2 for the third. Multiplying all this you get 4 x 3 x 2 = 24 options.
From left to right, pick the smallest possible digit every time. This will give you the smallest possible number.
It is: 8*12.5 = 100
it would be 0000.01
5040 numbers can be made.
4 options for the first digit, 3 options for the second digit, 2 options for the third digit. Multiply the number of options together, and you find how many 3-digit numbers you can get.
34, 45 etc.
There are 2 choices for every digit in the 6-digit number. So 26 is 2*2*2*2*2*2. The answer to that is 64.
Assuming that the first digit of the 4 digit number cannot be 0, then there are 9 possible digits for the first of the four. Also assuming that each digit does not need to be unique, then the next three digits of the four can have 10 possible for each. That results in 9x10x10x10 = 9000 possible 4 digit numbers. If, however, you can not use the same number twice in completing the 4 digit number, and the first digit cannot be 0, then the result is 9x9x8x7 = 4536 possible 4 digit numbers. If the 4 digit number can start with 0, then there are 10,000 possible 4 digit numbers. If the 4 digit number can start with 0, and you cannot use any number twice, then the result is 10x9x8x7 = 5040 possilbe 4 digit numbers.
874321 is the largest number made from all these digits.
Nope, look at 1000, this is a 4 digit number and we can't list it with 1,2,3, and 4
The possible 4 digit codes using the numbers 0-9 are every number between 0 and 9999. For numbers that have less than 4 digits, just precede the number with 0's. 10,000 possibilities