涛涛数学一道题，请指点，谢谢大家！

lijia1301981

Q2:

The function f is defined for each positive three-digit integer n by f(n) = 2^x3^y5^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) = 9f(v), then m-v = ?

 

A.   8

B.   9

C.   18

D.   20

E.   80

Answer: D

beforelq

因为你看x,y,z分别是它的百位，十位，个位，f(m) = 9f(v), 而且m和v都是三位数，也就是说f(m) =3^2f(v), 也就是f(m)的x，z和f(n)相等，

换句话说，就是假如f(m)=100x+10y+z,f(n)=100x+10(y+2）+z,也就是这两个三位数的百位和个位相等，但是m的十位数比n要大2.所以答案是20

lijia1301981

明白了，多谢高手了！