To determine how many three-letter "codes" can be made from the letters "FGHIJKLMNO" without repetition, follow these steps:

1. Count the number of available letters:
   The letters available are "FGHIJKLMNO", which gives us a total of 10 distinct letters.

2. Determine the number of choices for each position in the code:

   • For the first position, you can choose any of the 10 letters.
   • For the second position, since repetition is not allowed, you have 9 remaining letters to choose from.
   • For the third position, you have 8 remaining letters to choose from.

3. Calculate the total number of possible codes:
   Multiply the number of choices for each position: $10 \times 9 \times 8 = 720$

So, there are 720 different three-letter codes possible when repetition is not allowed.

Would you like more details or have any questions?

Here are some related questions you might find interesting:

1. How many four-letter codes can be made if repetition is not allowed?
2. What if only vowels are allowed in the code, and repetition is not allowed?
3. How many three-letter codes can be made if the first letter must be a consonant?
4. How many three-letter codes can be made if exactly two letters must be the same?
5. How does the total number change if you allow repetition for only the last letter?

Tip: When repetition is not allowed, the number of choices decreases with each position, making the calculation a simple product of descending numbers.