Question

why are repeated trails important in scientific investigations?

Answer 1

In order to obtain values which are near to the true value...

Answer 2

When you do an experiment, there are always situations that can change the result. If one of those situations comes into play during the experiment without you knowing, it can throw off the answer you get by a lot. If you do several trials, you'll be able to see that something went wrong, throw out that result, and average the rest together. That way, you know you're getting a fairly accurate answer.