We are currently doing permutations and factorials in my Maths course. In this week's online quiz there's a question that goes like this:
A DNA sequence can be represented as a string of the letters ACTG. Given a DNA sequence of length 26, how many double letter mutations are possible?
I have absolutely no background in Chemistry or Genetics so I think I'm interpreting the question incorrectly. Here's what I've tried:
- Picking two random positions and changing each of them:
26*3*25*3 - Picking two adjacent positions and changing each of them:
25*3*1*3
All my attempts have been marked as incorrect by the auto-marker. Any ideas?
Best Answer
Picking two random positions is ${26\times25\over2}$, not $26\times25$, so the answer they want is $${26\times25\over2}\times3\times3$$