Question

A ship carries exactly 10 different signal flags. If each possible combination and ordering of 4 of these flags connotes a specific message, how many signals can be
sent with these flags, taken 4 at a time?

Answer 1

If a flag can be used more than once in a signal, the number would be 10x10x10x10 = 10000

If a flag can be used only once, the number is
10x9x8x7 = 5040