1. The function f is defined for all positive integers n by the following rule: f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1. If p is any prime number then f(p)=
A. p-1
B. p-2
C. (P+1)/2
D. (p-1)/2
E. 2
这题描述f(n)那句话愣是没看懂。。。。
2. Marta bought several pencils. If each pencil was either a 23-cent pencil or a 21-cent pencil, how many 23-cent pencils did Marta buy?
(1) Marta bought a total of 6 pencils
(2) The total value of the pencils Marta bought was 130 cents
这题选B 没问题,但是除了凑数字有别的什么一眼就能看出来的方法吗?