Math 19-05 mừng sinh nhật một vĩ nhân

[Son]

http://www.binhthuan.gov.vn/KHTT/Vanhoa/0005/0000/images/BHo.JPG
3/5 of a certain class left on a field trip. 1/3 of the students who stayed behind did not want to go on the field trip (all the others did want to go). When another vehicle was located, 1/2 of the students who did want to go on the field trip but had been left behind were able to join.What fraction of the class ended up going on the field trip?

A. 1/2

B. 2/3

C. 11/15

D. 23/30

E. 4/5
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[quanie]

Vote cho câu C

[ndanh06]

one more vote for C
Em crack như sau:
- 3/5 left on field trip = 9/15 => stayed behind = 6/15
=> 1/3 of stayed behind did not want to go = 2/15 => did want to = 4/15
=> 1/2 of did want to were able to join = 2/15
=> End up going field trip = 9/15 + 2/15 = 11/15

Các bác thông cảm, vì em mới chập chững xơi gmat nên muốn giải thích kĩ càng tí, để có gì sai mong các cao thủ còn chỉ giáo giúp. Em cảm ơn trước ạ!