请教GWD-07-14

wangtsong

Q14:

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

Why not D. 'cos A55/A44=5？

对么？

A,B,C,D,....我没理解。

justsuperfro

(10*9*8*7*6)/(10*9*8*7)=6/1

wangtsong

oh, A10 5/ A10 4.