How many 4-digit numbers are there having all digits as odd? 

Counting 4-digit Numbers with All Odd Digits:

• Each digit in a 4-digit number can be one of the odd digits: 1, 3, 5, 7, or 9.
• There are 5 choices for each digit since there are 5 odd digits available.
• For a 4-digit number, we need to select a digit for each of the 4 positions independently.
• The total number of 4-digit numbers with all odd digits is the product of choices for each digit.

Calculation:

Given,

Choices for each digit = 5 (as the digits are 1, 3, 5, 7, 9)

Number of digits, n = 4

The total number of 4-digit numbers with all odd digits is,

\(5^4\) =  5 × 5 ×5 × 5 = 625

∴ 625 4-digit numbers have all digits as odd.5×5×5×5 5×5×5×\there

∴ The total number of 4-digit numbers with all odd digits is 625.