Q2:

The function f is defined for each positive three-digit integer n by f(n) = 2^x 3^y 5^z, where x, y, and z are the hundreds, tens, and units digits of n, respectively.  If m and v are three-digit positive integers such that f(m) = 9 f(v), then m - v =

A.     8

B.     9

C.     18

D.     20

E.      80

m=abc,v=xyz

f(m)=2^a*3^b*d^c=9f(v)=2^x*3^(y+2)*5^z

说明a=x,b=y+2,c=z

m-v=(100a+10b+c)-(100x+10y+z)=10(y+2)-10y=20

D