求NNprep 感到很白痴但是又解不出的题目··· thx··

xyqirene · 发表于 2010-12-8 20:38:29

If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

(A) 38

(B) 39

(C) 40

(D) 41

(E) 42

At a dinner party, 5 people are to be seated around a circular table.Two seating arrangements are considered different only when the positions of the people are different relative to each other.What is the total number of different possible seating arrangements for the group?

(A) 5

(B) 10

(C) 24

(D) 32

(E) 120

At a dinner party, 5 people are to be seated around a circular table.Two seating arrangements are considered different only when the positions of the people are different relative to each other.What is the total number of different possible seating arrangements for the group?

(A) 5

(B) 10

(C) 24

(D) 32

(E) 120

sdcar2010 · 发表于 2010-12-8 21:25:58

If each term in the sum a1 + a2 + . . . + an is either 7 or 77 and the sum equals 350, which of the following could be equal to n ?

(A) 38

(B) 39

(C) 40

(D) 41

(E) 42

For this one, you need to look at how many 7 add together can give you zero at the single digit. You have to have multiple of ten as the number for 7 to so do. Only C is a multiple of 10.

sdcar2010 · 发表于 2010-12-8 21:30:23

At a dinner party, 5 people are to be seated around a circular table.Two seating arrangements are considered different only when the positions of the people are different relative to each other.What is the total number of different possible seating arrangements for the group?

(A) 5

(B) 10

(C) 24

(D) 32

(E) 120

For this one, if put them on a straight line, the possible arrangements are 5! = 120. However, since it is a circle, you would have:
ABCDE = BCDEA = CDEAB = DEABC = EABCD
In other word, you count five different linear arrangements which are considered the same in the circular arrangement. 120 / 5 = 24

DeliciaAn · 发表于 2015-6-13 10:02:57

顶一下楼上的解释

求NNprep 感到很白痴但是又解不出的题目··· thx··

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