There are 9 digits that can be the first digit (1-9);
for each of these there is 1 digit that can be the second digit (6);
for each of these there are 10 digits that can be the third digit (0-9);
for each of these there are 10 digits that can be the fourth digit (0-9).
→ number of numbers is 9 × 1 × 10 × 10 = 900 such numbers.
1000... 0600-0699 1600-1699 and so on.
The first digit has 4 choices for its digit. The second digit has 6 choices and the third has 3. The solution would simply be 4*6*3=72 three digit numbers.
The second digit can be 2,4,6, or 8. There are 4 ways of choosing the second digit. The first digit can be chosen from the remaining 8 digits. 8x4 = 32 numbers. Here, it is assumed that the numbers do not repeat
24
17
The first digit can have 5 possible numbers, the second digit can have 4, the third 3, the fourth 2. 5
1000... 0600-0699 1600-1699 and so on.
4
The first digit has 4 choices for its digit. The second digit has 6 choices and the third has 3. The solution would simply be 4*6*3=72 three digit numbers.
The second digit can be 2,4,6, or 8. There are 4 ways of choosing the second digit. The first digit can be chosen from the remaining 8 digits. 8x4 = 32 numbers. Here, it is assumed that the numbers do not repeat
81 As there are no limits stated then you can have a number comprising a repeated single digit (such as 2222), two pairs of numbers (e.g. 2244) or three different numbers (such as 2462). The first digit can be one of any of the 3 numbers. The second digit can be one of any of the three numbers, as can the third digit and also the fourth. Then you can have 3 x 3 x 3 x 3 = 81 different 4-digit numbers using the three given numbers.
24
17
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.
3 digit numbers are lessthan 4 digit numbers
There are 2941 4-digit numbers such no two of its digits differ by 1.
There are 16 4-digit numbers that can be made up from 9 and 6.