一道搞不懂的数学题

florachu

A total of 100 customers purchased books at a certain bookstore last week.  If these customers purchased a total of 200 books, how many of the customers purchased only 1 book each?

(1)   None of the customers purchased more than 3 books.

(2)   20 of the customers purchased only 2 books each.

                  

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.

menghao0326

选C吧。。。。

sherry树丛

我选A正确答案是什么呀？

mickleon

For (1), because no one purchased more than 3 books, the possible number can only be 1/2/3.

And for only 100 people purchased ,[people brought 1 book]+[people brought 2 books]+[people brought 3 books]=100

Additionally, as we know the average (arithmetic mean) is 2, we can
directly know [people brought 1 book] must equal to [people brought 3
books]. But we still don't know the exact number.

    

For (2), if only 20 people purchased 2 books, this means [people brought 1 book]+20*2+[people brought 3 book]*3=200

    

So, only combining them together, we can work out [people brought 1 book]=[people brought 3 books]=40.

Yes, I mean "C" is the choice.

    

yidiyuehan

同意LS 的。

现在发觉数学要想在有限时间内拿高分也是不容易啊。

sherry树丛

呵呵。。。no MORE THAN 3 我没把3算进去。。。