Maths (M.C.)

2009-07-02 7:03 pm
Peter has to finish a job. He has finished 1/3 of the job in first working day and 3/7 of the remaining job in the second working day. What
fraction of the job remains?
A. 5/21
B. 8/21
C. 1/21
D. 13/21

回答 (5)

2009-07-02 7:12 pm
✔ 最佳答案
你好!
=1-1/3+3/7=?
=1-(7/21+9/21)
=1-16/21
=5/21
因此答案是A。

2009-07-02 13:30:28 補充:
i am not a 知識長= =
2009-07-02 7:53 pm
第一天完成了1/3,餘下2/3.
第二天完成餘下工作的3/7,即完成了2/3 x 3/7 = 2/7
兩天共完成了 1/3 + 2/7
= 7/21 + 6/21 = 13/21
所以餘下的比例是 1 - 13/21 = 8/21 (答案:B)

2009-07-02 12:11:51 補充:
3/7 of the remaining job是餘下工作的3/7,不是整件工作的3/7。

2009-07-02 13:59:42 補充:
3/7 of the remaining job的意思是說剩下來工作的3/7,不是說原有工作的3/7.

2009-07-02 14:13:23 補充:
留意, 不要誤解了題目:3/7 of the remaining job是說餘下工作的3/7,不是整件工作的3/7.

2009-07-02 14:15:26 補充:
留意,3/7 of the remaining job的意思是餘下工作的3/7,不是整件工作的3/7.

2009-07-02 20:47:09 補充:
留意,3/7 of the remaining job的意思是餘下工作的3/7,不是整件工作的3/7.
2009-07-02 7:41 pm
After the first day, remains: 1-1/3 = 2/3 of the job

After the second day, remains: 2/3 - 3/7 = (14-9)/21 = 5/21 (A)
2009-07-02 7:17 pm
1-1/3-3/7

=21/21-7/21-9/21

=14/21-9/21

=5/21

So A. is correct

2009-07-03 09:21:35 補充:
Sorry,搞錯方法計。

第一天完成1/3,第二天只完成:(1-1/3)x3/7=2/7

故剩下:1-1/3-2/7

=2/3-2/7

=14/21-6/21

=8/21

B才對
2009-07-02 7:13 pm
The fraction of the job remains

1-1/3-3/7

=21/21-7/21-9/21

=14/21-9/21

=5/21(A.)


hope I can help you~
參考: mememe


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