What if you could do something small, today, and have it add value for the rest of your life?
By memorizing these key numbers, you can permanently eliminate the tiny-but-frequent task of looking them up every time you need them. The same way that having more RAM in your computer makes your computer run faster, having a more useful working memory in your head can help you conquer day-to-day tasks with relative ease, freeing you to solve newer (and more valuable) problems.
Memorize these numbers once, and it’ll pay dividends the rest of your life!
Being able to wrap up an online order without having to reach for your wallet is going to eliminate a small hassle you probably face multiple times per week. You can easily memorize your credit card number – just take it a few digits at a time, and practice on your way to/from work. Next time you order Thai food for a late night in the office, notice how impressed your coworkers are as you effortlessly speak your credit card number into the phone!
If you ever find yourself computing interest rates on the fly (and hopefully you do, young baller), this one is for you.
The rule of 72 is a super easy method for estimating the amount of time an investment (or debt) will take to double in value. Say that you invest in something that has a 10% annual interest rate – how long does it take to double? The rule of 72 goes like this: 72 / 10 = 7.2 years. The actual answer is 7.3. Pretty close! Below are some calculations using the rule of 72 compared to the mathematically precise answer.
The actual way to solve it is x = log(2) / log(1+interest rate). Of course you should calculate it precisely if you’re in front of a computer, but the beauty of the rule of 72 is you can get in the ballpark in a split second.
If you’re a US citizen, your social security number is one of the primary ways that the US government identifies you. Taxes, new jobs or apartments, and other important business paperwork often requires your SSN. You don’t want to be blocked on filling out some paperwork just because you’re missing one piece of information. It’s great if you can avoid carrying your Social Security card around with you, since losing it exposes you to identity theft, and the United States Social Security Administration officially limits the number of social security cards you can get in a lifetime to 10.
Sometimes working professionals know their salary, but don’t know how to value their time hourly (or vice versa). A really handy conversion, assuming a full 40 hour week and 50 weeks in a year, is [hourly pay]* = annual salary. So if you make $60k in a year, working 40 hour weeks, you’re getting paid $30/hr. On the flipside, if you make $80/hr, you’ll make $160k in yearly salary.
When you’re travelling, you use your passport number all the time – on customs forms, at hotels/hostels, renting cars, etc. It’s one of the most valuable things you have on you. The less that you need to pull it out, the better you’re able to manage risk of leaving it / losing it / having it stolen.
There you have it! Take the time to memorize these numbers once, and you’ll have them at your disposal for the rest of your life. Another quick tool for keeping single-use numbers (hotel room number, security code to an office) is to dial the number on your phone and then hang up. No need to open an app and make a note that number you’ll only need once anyway – you’ll find it easily in your call history.
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