求GWD的几道题

kaipiggy

1.If n is a positive integer and r is the remainder when (n – 1)(n + 1) is divided by 24, what is the value of r?
(1)2 is not a factor of n.
(2)3 is not a factor of n.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

答案是C，穷举可以得出，可是为什么呢？


2.Of the fruit that arrives at a cannery, 20 percent by weight is rejected before processing.Of the fruit that is processed, 15 percent by weight is rejected before canning.Of the fruit that arrives at the cannery, what percent by weight is canned?


A.32%
B.35%
C.65%
D.68%
E.70%

答案是D。不解题目意思。。。

请NN解答！

horses530

20 percent by weight is rejected before processing............所以80% is processed
Of the fruit that is processed(80%), 15 percent by weight is rejected before canning
所以80%processed之中的85% is canned
所以最後就事80%*85%=68% is processed and canned

horses530

第一題就一個一個列出來看囉~
條件一：2 is not a factor of n.........所以n為奇數
條件二：3 is not a factor of n.........所以n不為3的倍數
兩個分開都不能求得~所以把兩個條件中都有列到的數代進去算就可以算出來了~

kaipiggy

谢谢~~~~~~~~~~~~~~