[求助]一道数学题（）

ztlbox

（不知出处）

Larry saves x dollars per month. Will Larry’s total savings one year from now exceed his present savings by at least $500 ? (Assume that there is no interest.)

(1) In 6 months Larry's total savings will be $900.

(2) In 3 months Larry's total savings will exceed his present savings by $150.

答案是b,不明白，total savings 包括present savings 吗？

我觉得应该是c.

beautywawa

ANS:B

條件(1)...In 6 months Larry's total savings will be $900

只是說他存下來的錢總共是900..可是我們並不知道說his present savings是多少

所以條件(1)不充分

條件(2)...In 3 months Larry's total savings will exceed his present savings by $150

已經說了..3個月的時候..就已經超過his present savings的150了..

所以150*4=600...12個月過後..就是600元..

就至少有超過his present savings500元......所以條件(2)充分

ztlbox

偶理解是过去存的加上3个月存的比过去存的多150来着，不过看来不影响结果

一直算4*150=450来着，

唉，看来只有哈佛会要偶了--------------哈尔滨佛学院（哈佛）

beautywawa

別這樣...

不會的啦..

大家一起討論..