GWD(31套)-7-14

7-14.If a code word is defined to be a sequence of different letters chosen from the 10 letters A, B, C, D, E, F, G, H, I, and J, what is the ratio of the number of 5-letter code words to the number of 4-letter code words?

A.     5 to 4

B.     3 to 2

C.     2 to 1

D.     5 to 1

E.      6 to 1

Answer:E

怎么算的

this question is testing the concept of "Permutations" not "combinations".

the total number of 5 letter codes: 10!/(10-5)!=10*9*8*7*6

the total number of 4 letter codes: 10!/(10-6)! = 10*9*8*7

the ration is 6 to 1 =>ansnwer E