Question

How many five letter codes can be made if no letter can be used twice

Answer 1

The aritmetic sequence has the characteristic that each term is the term before plus a constant number. Then we can create the following system of equations:

`\begin{gathered} x-34=p \\ 345-p=x \end{gathered}`

where p is the constant value which is added in each term, and x the number between 34 and 345. If we replace the value of "x" from the second equation into the first one:

`\begin{gathered} 345-p-34=p \\ 311=2p \\ 155.5=p \end{gathered}`

Finally, the term betwen 34 and 345 is 34+p, 189.5

Hence the answer is 189.5