i have a problem in understanding a combinatorics formula in my algebra book.
hope i am posting in the right section, i found no section on combinatorics,sorry.
it says that the no of permutations of n different things taken r at a time ,when p particular things are to be always included in each arrengement is
p! (r-p+1) ((n-p) permutation (r-p))
i proceeded in the following way-let me first find the arrengements of the things other than the p ones. that is n-p P r-p.
now the p things can arrenge in p! ways.
but i cannot understand how (r-p+1) is coming here.
thanks in advance for any help.