Question

Use formula for permutations to calculate in how many ways you can select 2 people out of 10,

Answer 1

The formula for permutations is
  P(n, k) = n!/(n-k)!

For n=10 and k=2 the formula tells you
  P(10, 2) = 10!/8! = 10*9 = 90
there are 90 ways to select 2 people from 10 when order matters.