Any number that has 4 or 5 digits. A digit in a number is one number place. 1 has 1 digit, 11 has 2 digits, 111 has 3 digits, and so on.
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
40,000, 80,000
8000
1000
5*5*4*4 = 400
9
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