math
posted by marie on .
use the formula nPr to solve
how many arrangements can be made using four of the letters of the word COMBINE if no letter is to be used more than once?

The 7 letters of the word "COMBINE" are distinct, so there are 7 choices for the first letter, only 6 for the second, 5 for the third, and 4 for the fourth.
Since the choices are independent, by the rule of multplication, the number of choices is:
7*6*5*4
=? 
840

840