# Math Help - Probability: No. of 4-letter string formed by ...

1. ## Probability: No. of 4-letter string formed by ...

Question

How many no. of 4-letter strings can be formed by the letters {A,B,C,D,E,F} with no repetitions and A cannot be the first letter?

I know the total no. of 4-letter strings with no repetitions is 6x5x4x3=360

Then it comes to the next consideration: how many no. of combination with A being the first letter...

Should it be 5x4x3=60?[/SIZE]

Not sure if this is correct ...

2. Originally Posted by pozat
Question

How many no. of 4-letter strings can be formed by the letters {A,B,C,D,E,F} with no repetitions and A cannot be the first letter?

I know the total no. of 4-letter strings with no repetitions is 6x5x4x3=360

Then it comes to the next consideration: how many no. of combination with A being the first letter...

Should it be 5x4x3=60?[/SIZE]

That is correct. It is also $5\cdot 5\cdot 4\cdot 3=300$