xiaotantan

a drop in the ocean  沧海一粟，九牛一毛
ki11 two birds with one stone 一箭双雕
A fall into the pit, a gain in your wit. 吃一堑长一智
at sixes and sevens  乱七八糟
Two heads are better than one.  人多智广
His mark in math is second to none in the class. 他的数学分数在班上是数一数二的
She is a second Lei Feng. 他是第二个雷锋
I always believe my sixth sense.  我总相信我的第六感觉
He talks about you nine times out of ten when we have a chitchat.  
当我们聊天时他十有八九会谈到你