[問題]Prep math

[whoops]

Is m + z > 0 ?
1. m - 3z > 0
2. 4z - m > 0

答案是C

(1) m > 3z...條件不足
(2) 4z > m...條件不足
(1)+(2) 4z > m > 3z.....

哪位指點一下...thanks

[weirdude]

I have the same logic as u do.
Now, I think more about it.
since 3z<m<4z
and 4z-m>0
therefore, 4z-(3.xxx)z>0 and it leads to z>0.
Hence, m>0 as well.
here you got ur answer "C".

[whoops]

Is m + z > 0 ?
1. m - 3z > 0
2. 4z - m > 0

答案是C

再想了一下
(1)+(2)可以得出
m-3z+4z-m>0
整理一下可得z>0再帶回(1)
可得m>0
故m + z > 0
不知這樣思考有沒有誤謬