A random sample or method is one in which all the people or things involved have an equal chance of being chosen.
targeted
The survey used a random sample of two thousand people across the Midwest.
这项调查在中西部地区随机抽取了2000人。
The competitors will be subject to random drug testing.
参赛者将接受随机的药物测试。
If you describe events as random, you mean that they do not seem to follow a definite plan or pattern.
random violence against innocent victims.
对无辜受害者的任意攻击。
at random
If you choose people or things at random, you do not use any particular method, so they all have an equal chance of being chosen.
We received several answers, and we picked one at random.
我们收到了好几个答复,就随机地拣选了一个。
If something happens at random, it happens without a definite plan or pattern.
Three African-Americans were killed by shots fired at random from a minibus.
3名非洲裔美国人被从一辆小型公共汽车中胡乱射出的子弹打死了。