简单数学3到 求帮忙

guo573874201

1. Theater M has 25 rows with 27 seats in each row.How many of the seats were occupied during a certain show?
(1)During the show, there was an average (arithmetic mean) of 10 unoccupied seats per row for the front 20 rows.
(2)During the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for the back 15 rows.答案选E   思路是什么
2. The total cost of an office dinner was shared equally by k of the n employees who attended the dinner.What was the total cost of the dinner?
(1)Each of the k employees who shared the cost of the dinner paid $19.
(2)If the total cost of the dinner had been shared equally by k + 1 of the n employees who attended the dinner, each of the k + 1 employees would have paid $18.     需要思路  答案C

3. This year Henry will save a certain amount of his income, and he will spend the rest.Next year Henry will have no income, but for each dollar that he saves this year, he will have 1 + r dollars available to spend.In terms of r, what fraction of his income should Henry save this year so that next year the amount he was available to spend will be equal to half the amount that he spends this year?答案E

   A 1/r+2     B  1/2r+2     C 1/3r+2    D 1/r+3   E  1/2r+3
    球思路    拜托了

bbfcsak

第一题我觉得可以算出来啊~
1+2,可以得出有10排是重复的，根据条件1，那么前面20排的人数是20X17=340。条件2，后面15排应该是15x7=105人。
那么你找极端啊，就算最前面10排全部坐满人，也就是说前面10排是270个人，那么为了满足条件1，中间10排还可以坐70个人。然后为了满足条件2，因为中间10排已经有70人了，那么后面5排必须有35人才能达到标准，所以总人数就是270+70+35=375人。所以选C啊！
第二题我觉得是无解的啊。
根据条件1，每个人要交19，那么总共是19K，然后总共就是19N的COST
根据条件2，每个人要交18+1，那么总共还是19N的cost啊，没有N求不出啊。。
1+2照样无解啊
第三题我真心不会做，题目好歹给个第一个月工资总数才好算。

Edwina熊熊

第三题：
设今年花钱X，存钱Y，总收入则为X+Y
明年可以花的钱是今年存得（1+R）倍，是Y(1+R)
明年可以花的钱是今年可以花的钱的一半，则，Y(1+R)=X/2
所以X=2Y(1+R)
总收入是X+Y=2Y(1+R)+Y
今年存钱所占比重是Y/(X+Y)=Y/(2Y(1+R)+Y)=1/(3+2R)
选e

bbfcsak

实在是画龙点睛，我明白了。

Edwina熊熊

第二题，
我觉得总体N人就是个迷惑条件，没有用处。
1. K人参加，每人19，总花费19K
2. K+1人参加，每人18，总花费18（K+1）
1+2
总花费不变，19K=18（K+1), 求出K=18
一顿饭总共花=19*18
选C
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
第1题，我不确定
前20排，平均每排空10个，则一共空200个，设为集合A
后15排，平均每排空20个，则一共空300个，设为集合B
集合A与B有交集，就是中间那10排，并不知道具体空多少，交集可大可小，无法准确判断
这情况就像韦恩式图那个交集的情况，不知道中间重叠部分是多少，所以选E