Kids and adults alike acknowledge that we use elementary-school math in real life on a daily basis. We add, subtract, multiply and divide quite frequently. But when teachers start replacing the numbers with letters, and are introduced to terms such as "variable" and "polynomial", then those instructors meet resistance from students, and their protests often center around the idea that this kind of math will do them no good in the real world.
A lazy adult will simply affirm the students' suspicions by admitting that complex algebraic problems don't make their way into everyday life. It's an easy thing to say, but the truth is that life is full of situations in which formulas are required or at least helpful.
Here are some math formulas that ring true in real life:
Real-life application: The size of a pickup truck is inversely proportional to the likelihood that the driver is a cat owner.
Where "C" is the likelihood that the driver is a cat owner (the dependent variable), and T is the truck size (the independent variable). As T increases, C decreases.
G = A - (C + RE)/O
Real-life application: If you've ever grocery-shopped, you are aware of the Obvliot, the one who blocks the aisle by having their cart on one side, and their body on the other. Shoppers like you need to be able to calculate the available space in order to determine whether to try to get through, or just go around.
-G stands for the Gap that you can drive your cart through.
-A is the width of the aisle
-C is the width of the cart
-RE is the width of the Rear End of the shopper who's trying to keep you from making progress in your journey.
and of course
O is the measure of how Oblivious the shopper is to the fact that they are in the way.
Where A is the amount, in gallons, of perfume that is applied to the offender's face/neck/whatever, where P is the perfume, and SF is the Stink Factor.
Do you have any more math formulas which apply to real life?