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Numbers & Conversions?

Cups, miles, percentages. The stuff you re-Google forever. 28 questions and counting.

How do you convert Celsius to Fahrenheit?Exact: multiply by 9/5 and add 32. Fast enough for weather: double it and add 30. And the anchor points to memorize: 0C is…
How do you calculate a tip in your head?Move the decimal one place left for 10 percent, then add half of that for 15 or double it for 20. On a $46 check: 10 percent…
How do you read a nutrition label?Start with serving size, because every number below it is per serving, not per package. Then check added sugars and sodium…
How many cups are in a gallon?16 cups in a gallon. The full ladder: 2 cups to a pint, 2 pints to a quart, 4 quarts to a gallon. Everything doubles, which…
How many feet are in a mile?5,280 feet. The odd number is Rome's fault mixed with England's: a Roman mile of 5,000 feet got stretched to fit exactly 8…
How many weeks are in a year?52 weeks plus one extra day, or two in a leap year. That leftover day is why your birthday shifts one weekday each year, and…
How do you calculate a percentage?Part divided by whole, times 100. And for mental math, flip stubborn ones: x percent of y equals y percent of x, so 4…
What is a good credit score?On the common 300 to 850 scale, roughly 670 and up is good, 740 and up is very good, and 800 and up is exceptional. Payment…
What is the order of operations?Parentheses, exponents, then multiplication and division left to right, then addition and subtraction left to right. The…
How much bigger is a trillion than a billion?A thousand times bigger, which is nearly impossible to feel. In seconds: a million is about 12 days, a billion is about 32…
What is the difference between mean, median, and mode?Mean is the average, median is the middle value, mode is the most common. Median beats mean whenever a few extreme values…
How do you calculate a discount in your head?Take 10 percent by moving the decimal, then build. 30 percent off a $45 item is three lots of $4.50, so $13.50 off, leaving…
What is the difference between correlation and causation?Correlation means two things move together; causation means one produces the other. Two variables can correlate because a…
What is exponential growth, and why is it so hard to picture?Growth by a constant percentage rather than a constant amount, so the increase itself keeps increasing. Human intuition is…
How do you calculate square footage?Multiply length by width for each rectangular section and add them together. For odd shapes, break the room into rectangles…
How do you convert fractions to decimals and percentages?Divide the top by the bottom to get the decimal, then multiply by 100 for the percentage. Three quarters is 3 divided by 4…
How do you fairly split a restaurant bill?Split evenly when orders are similar and it saves everyone time. When one person had an appetizer, two drinks, and the…
What does statistically significant actually mean?That a result is unlikely to have arisen by chance alone under the assumption of no real effect, conventionally at a p-value…
What is a prime number?A whole number greater than 1 divisible only by 1 and itself: 2, 3, 5, 7, 11. They are the atoms of arithmetic, there are…
What does average annual return actually mean?Usually the compound annual growth rate, the steady rate that would produce the same end result, not the simple average of…
What does margin of error mean in a poll?The range within which the true value probably falls due to sampling alone, usually at 95 percent confidence. A 3-point…
What is pi, and why does it matter?The ratio of any circle's circumference to its diameter, about 3.14159, and it is the same for every circle regardless of…
What is the difference between weight and mass?Mass is how much matter something contains and never changes; weight is the force gravity exerts on that mass and changes…
What is the rule of 72?Divide 72 by an annual growth rate to get the years it takes to double. At 6 percent, money doubles in about 12 years. It…
Why is a day 24 hours and an hour 60 minutes?Egyptians split day and night into 12 parts each, likely using a base-12 counting system on finger joints. The 60-minute…
What is the difference between APR and APY?APR is the annual rate without compounding and is used for what you borrow. APY includes compounding and is used for what…
What is the golden ratio, and is it really everywhere?An irrational number about 1.618 with genuinely interesting mathematical properties and a real presence in some plant growth…
How do you estimate a square root in your head?Find the nearest perfect squares on either side and interpolate. For 60, you know 49 and 64, so the answer is just under 8…