5
There are 9000 4-digit numbers. 8*9*9*9 = 5832 of them do not contain a 5 The remaining 3168 contain a 5.
4
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
1000
5
The first digit can have 5 possible numbers, the second digit can have 4, the third 3, the fourth 2. 5
There are 9000 4-digit numbers. 8*9*9*9 = 5832 of them do not contain a 5 The remaining 3168 contain a 5.
4
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
There are 2000 4-digit numbers that are multiples of 5, so, instead of listing them all, it is equally valid to say: Any4-digit number whose final digit is either a 5 or a 0 is a multiple of 5. Get Right? :P
To find the number of 4-digit numbers with only odd digits, we need to consider the options for each digit. Since odd digits are 1, 3, 5, 7, and 9, there are 5 choices for each digit. Therefore, the total number of 4-digit numbers with only odd digits is calculated as 5 x 5 x 5 x 5 = 625. So, there are 625 4-digit numbers that have only odd numbers.
40,000, 80,000
1000
8000
There are 4 options for the hundreds digit (3, 4, 5, or 6), and 4 options for the tens digit (including the possibility of repeating the hundreds digit). Similarly, there are 4 options for the units digit. Therefore, the total number of 3-digit numbers that can be formed using the digits 3, 4, 5, and 6 with repetition allowed is 4 x 4 x 4 = 64.
20 There can be two answers to this: I'll assume this is what you meant-> let's say you mean like pairing the numbers 1-5 with the numbers 6-9. 5*4=20