Question

Why is it important to have complex carbohydrates before a big race?

(Again, not math. I know, its to get the answer faster..)

Answer 1

Complex Carbs are very useful because they are healthy and do not interfere with a race. They turn those into glucose and helps the energy be saved longer. 

Answer 2

Complex Carbohydrates are made up of sugar molecules strung together in long chains. Both simple and complex carbs can be turned into Glucose which is used as short term energy. This short term energy is great for short races, for marathons I suggest more lipids as well. The act of eating a lot of carbs the night before a race is called "Carb Loading"