求教两道数学题

Q6:

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

答案D

A certain characteristic in a large population has a distribution that is symmetric about the mean m.  If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m +
                d ?

A.     16%

B.     32%

C.     48%

D.     84%

E.      92%

答案 D

实在没看懂题意, 求教给予解释

1.f(v)=2^x*3^y*5^z,f(m)=9f(v)=2^x*3^(y+2)*5^z

v=100x+10y+z,m=100x+10(y+2)+z

m-z=20

2.(m-d)~(m+d) = 68%

<=(m+d) = 1-(1-68%)/2=84%