1. During a trans-atlantic trip ticket, 20% held round-trip and with cars aboard, 60% held round trip ticket with no car aboard. ask the total percentage of persons held round-trip ticket.
30%, 60%, 66-1/3 %
2.DS题，这道题我起码用了5分钟，有一种新药，对人有效也有时有副作用至少对10%的人有效，在有效的人中，有60%的人有副作用，问
是对有效的人多还是有副作用的人多
A.对90%的病人有效
B 在有副作用的人中，对10%有效
these possibility problems always confuse me...
anyway ,
1. 50%
60% held round trip ticket with no car aboard.=> 40% held round trip with car aboard
set tatoly x ppl hel round trip
x*40%=20%
x=50%
2. I incline to choose A
but wonder how to use 至少对10%的人有效
since with A
those have side effect = 90%*60=54%
even though all the other 10% on whom the medicine has no effect , no more than 64% of the ppl will have side effect from the medicine always less than the 90% on whom the medicine will have effect
