Real World Math: Close Enough
My dad used to say “close only counts in horseshoes and hand grenades”, however in the vast majority of everyday math that we use throughout our lives we rely on “close enough” a lot more often than we do getting the kind of very specific answer that’s demanded of us in math class.
In fact, using the “close enough” vs. “not close” evaluation will suffice in almost every math-related situation most people will encounter in life unless they’re an engineer or statistician.
For You & Older Kids
- Quarter of a tank of gas on Friday morning? Good enough to get to work and back.
- It’s irrelevant that you can drive exactly 63.4 miles with the remaining fuel in your tank – work is only 8 miles away.
- Grocery shopping for the week and you only have a $20 in your wallet? Better hit the ATM.
- Unless you’re planning to live on bread and rice, you’re probably going to spend at least $50-$100 on groceries.
- Thinking about buying a lottery ticket? The odds are so great against you that you’d literally be better off burning that dollar for warmth.
- You’re more likely to get struck by lightning – twice – than win the Powerball lottery.
- You and three friends want to order a pizza that costs $10. You’ve got $3, one friend has $2.65, another $2.92, and the other $3.17.
- The smallest amount anyone has is more than 1/4th the cost of the pizza, so you’ve got enough to put your order in.
Moreover, learning how to quickly figure out what the approximate answer is to a math problem also comes in very handy in school – especially on standardized tests. Here’s an example:
What’s 22,020 / 735?
If you can estimate what the correct answer might be, you can quickly eliminate at least one, usually two and sometimes all three incorrect answers without ever lifting your pencil. Let’s look at how to do this, using just the first digit of each number:
a) 45…what we want to do here is say “well, what’s 40 x 700?” – we’re removing the smaller digits to simplify. So 40 x 700 = 28,000. That’s too big. Notice that this also immediately eliminates d) as it’s higher than 45 to begin with.
b) 21…we simplify again and say “20 x 700 = 14,000” – not nearly enough. Consequently the answer must be c) because all others have been eliminated.
Many math sections on the major standardized tests such as the SAT, GRE, etc. actually require you to be able to do this kind of quick estimation on the simpler problems in order for you to have the time needed to really work out the tougher ones.
One final place that estimation can come in very, very handy is whenever you’re thinking about buying something on credit that you won’t be able to pay off immediately: with a 19%-24% APR credit card (pretty standard when just starting out), you can just multiply whatever you’re thinking about buying by 3 to get the final cost:
- $69.95 running shoes? Actual cost $210.00
- $13.99 CD? Actual cost $42.00
- $479.99 flat screen TV? Actual cost $1,440.00
Looked at this way, many of your wants can probably be delayed a bit until you have the cash – understanding credit and its cost to your future purchasing power is a discussion sorely lacking in most American economics classes – using this handy “3 times the cost” shorthand to envision the real long term cost of buying something you can’t afford in the moment.
For younger kids
A few simple estimation exercises can build the ability to get “close enough” to the answer as well as demonstrate the power of estimation:
- Pour a bowl of cereal and get out a 1 cup measuring cup, a quart Tupperware container, and a gallon of milk. Which one will give you enough milk for your cereal without being too much?
- Take a handful of change (maybe $2 worth at the most) and have them sort it by coin value (penny, nickel, dime, etc.) and then have them quickly figure out if they have enough for a $5 toy.
- Have them run a short course – maybe around the outside of the house (something that takes about 30 seconds to cover) and show them their time after lap 1. Ask if based on that they’ll be able to do 4 laps around the the course in 4 minutes? In 3?
So unless your kid is a 5th grade engineer or statistician, make it a point to get them accustomed to estimation. “Close enough,” in the realm of Real World Math, usually is.