To Be The Fastest Calculator In Any Room

To find out how much you’ll pay for an item that’s a certain percentage off, first subtract the percent off from 100. So if it’s 30 percent off, use 70; 60 percent off, use 40, etc. Divide this number and the price by 10 and then multiply the resultant two numbers. For instance, if a $20 shirt is...

Use the rule of 72 to calculate how long it would take an investment to double. The rule of 72 is that an investment that earns 10 percent interest will double in 7.2 years. Use this as a starting point for calculating various interest rates and lengths of time, by dividing the number 72 by your ...

To calculate how much a month more you’ll pay in a mortgage payment for a certain increase in house price, figure roughly 6 dollars per month for every thousand dollars more in total price.

Example : So for a house price that’s $30,000 more than another, you’ll pay $140 mo...

For quick conversions between Fahrenheit and Celsius: Celcius x 2 + 30 = Fahrenheit and (Fahrenheit – 30) / 2 = Celsius.

Convert an hourly wage to a salary by using the formula that $1 per hour is $2,000 per year.

Example : If you make $10 per hour, that would translate to a $20,000 per year salary.

Another way to compare hourly wages to a salary is to drop the three zeros of a salary ...

To estimate the annual cost of a daily habit, multiply to find the weekly total amount you spend (so, times 5 if it’s a weekday habit, or times 7 if it’s every day a week. Then add two zeros to that number, and divide by two.

Example : A $12 a day lunch five days a week w...

To quickly and roughly figure out what number you need to make a certain average, add together how far off you were from your target in each instance. Then add that resulting number to your target average for your final chance.

Example : If your scores are 90, 90, 85, and...

I suck at math, but I don't want to be disadvantaged in real world challenges.

Even in an age of smartphones, crunching numbers quickly — and getting good at it — can give you snappy, useful answers to pressing real-life math questions such as, Is this shirt a good deal? or How...