Economics

I just finished answering some questions for a Economics project about demand elasticities for a solar cell phone charger. I had to figure out the demand elasticities concerning price, substitutes, income level of cosumers, profitability...I have to ask myself, as I am sure many of us do when we are in school. WHEN AM I GOING TO USE THIS STUFF? I wonder,whenm working for company X, and I need to justify expense based on economic conditions, do I just think about it for a bit look over some numbers and file a report based on my findings OR do I mathematically calculate(in economic terms) the demand elasticites, calculate using more algebra than I will ever understand, and thern graph it out using letters based on both the English and Greek alphabets? Probably the first option. Then please someone explain to me why I need to know all this worthless crap I will never use and why I am paying $2100 to learn it.