Find the greatest three-digit odd number that can be formed from 2, 1, and 4.
Since the number is odd, the digit in the units place must be 1, 3, 5, 7, or 9. So, use the digit 1 in the units place.
Since we want the number to be as great as possible, use the greatest number in the hundreds place: 4.
The remaining number (2) belongs in the tens place.
So, the number 421 is the greatest three-digit odd number formed from 2, 1, and 4.