Why are repeated trials important in scientific investigations? what should you do if repeated trials give very different results?

They are important because scientists can not rely on just one experiment and conclude the result.Trace back the variation in results of different trials.

Explanation:

Whenever scientists conduct a scientific investigation, they don't stop at just only one experiment often what they do is repeating their experiments. And it's important because factors don't remain the same all the time and some variables which are not under control of a human can change time to time. Variables like weather, human behavior, etc aren't fixed they would change. Moreover, scientists are not perfect, they are humans and they do make mistakes so to prevent that, can be another reason for repeated trails. What if there are different results from every trial? Well, first of all, that is a good thing there is no way one can get the perfect answer in a first try. So what can be done is that start looking at differences in the results and get to know where the problem exists or what is being missed. Take an example of a balance sheet, whenever the balance sheet is not equal I tend to study the difference and track it back from the bottom to top to examine that, the area of the mistake. And when I finally understand that, then I try to understand why I have avoided it or why it should have been included.  

The answer is society was a caste like system with poor whites at the bottom of the white social ladder.