# Math Outside the Classroom

A common question instructors face from students is about the practical application of the topics they are learning in school or for the ACT or SAT: When will I need to know this in REAL life? I’ve often heard students express that they’ll never use a mathematic principle, like the quadratic formula, after their class.

And sometimes, students have a point. Do I use, or even remember, what I learned from AP Calculus in my day-to-day life? Nope. But, I do find myself often using math principles learned throughout school.

Wouldn’t it be nice not to have to ask Siri or Alexa for everything? Exercise your brain.

### Here are 10 common ways we use math in “real life:”

1. Time for the Check: How are you going to split the check when one person has a twenty dollar bill, one person Venmoed ten dollars, and the other two are paying by card? What percentage should you tip the waiter?

2. Discount Shopping: If you buy 4 items (one is 50% off, one is 30% off, and the store is doing 45% off your entire purchase), then how much will your total be?

3. ETA: If you left your phone at home but need to know how long it will take to travel a given distance. What’s your estimated time of arrival?

4. Gas Mileage: You just passed a sign that says you have 100 miles until the next gas station. You have 3 bars of gas left (each bar represents ~25 miles per gallon but ~30 miles per gallon on the freeway). You are uncertain how big your reserve tank is. Will you make it?**

5. Pay Rate: If you work this many hours a week at this rate for this long, how much are you making per minute? How much of a raise should you ask for to meet your expenses?

6. Exchange Rate: When traveling to another country, calculating exchange rates correctly is important. If you know the exchange rate is 1.12 euros for every American dollar, then how much would ordering another entree cost?

7. Metric to US Measurements: If you’re driving to Toronto, Canada, and it’s 60 km away, but your car tells you gas in miles per gallon, will you need to fill up before reaching Toronto? (And, then, you’ll have to calculate the exchange rate on the gas prices.)

8. Student Loans: If you don’t pay them, how much interest will accrue over a one year span? What’s a good interest rate versus a bad interest rate?

9. Floor: If your family wants to replace your downstairs flooring with wood, how much flooring do you need, including the weird triangle corners? How much is it going to cost you given this rate?

10. Hanging Pictures: If you measure the wall and know you’re going to hang four pictures and want them equal spaced, how big of a gap should you leave between them? Also, do you remember how to correctly add and subtract fractions?

**In case you’re curious, this happened to me while driving across Utah, and we did make it to the gas station, nicely surprised by the reserve tank of my car.