What is a rounded number?

Answer 1

For very large numbers and very small numbers, often people don't need the exact number as much as they need a close answer. For example, saying more than six billion people live on earth is more common than the exact number of people.

We round UP the numbers that end in five, and the others down.

104 rounds down to 100, but 105 rounds up to 110.

You can do this at any point in a number, as long as people are okay with you rounding.

1,264 rounds to 1,260 if you round the four down, to 1300 if you round the six up. You could even round the two down and say 1000.

Just remember that five through nine means you add, and one through four means you subtract.

Typical rounding problems are

• approximating an irrational number by a fraction, e.g. π by 22/7;
• approximating a fraction with periodic decimal expansion by a finite decimal fraction, e.g. 5/3 by 1.6667;
• replacing a rational number by a fraction with smaller numerator and denominator, e.g. 3122/9417 by 1/3;
• replacing a fractional decimal number by one with fewer digits, e.g. 2.1784 dollars by 2.18 dollars;
• replacing a decimal integer by an integer with more trailing zeros, e.g. 23,217 people by 23,200 people; or, in general,
• replacing a value by a multiple of a specified amount, e.g. 27.2 seconds by 30 seconds (a multiple of 15).