Basic Math: Rounding Off, Adding and Subtracting Numbers, Online Calculators

Three online calculators available: [+] Adding numbers [+] Subtracting numbers [+] Rounding off numbers

Calculations are followed by detailed step-by-step explanations:

1. Adding and subtracting natural numbers, 2 available calculators:

2. Rounding off numbers, 1 available calculator:


How to add natural numbers?

Method used: column adding, from right to left (traditional)

  • Stack the numbers on top of each other.
    • The ones digits line up in the first column from the right.
    • The tens digits line up in the next column to the left and so on...
  • Add column by column; start with the column on the right
    • Add the digits in the ones column.
    • Change the order in which the numbers are added, the sum stays the same. Break some number(s) into component parts, the sum stays the same.
  • If the sum above is a two-digit number:
    • Write the ones digit down at the base of the ones column.
    • Carry over the tens digit to the tens column. Write this digit above that column.
    • Add it with the rest of the digits in that column.
  • If the sum is a one-digit number:
    • Write the ones digit down at the base of the ones column.
  • Then add the digits in the tens column, exactly as you did for the digits in the ones column.
    • You can change the order in which the numbers are added and the sum stays the same. Or break some number(s) into component parts, the sum stays the same.
  • If you have more columns to the left (hundreds, thousands, and so on), continue with the addition exactly as you did with the ones column.

>> How to add natural numbers: calculate the sum and learn to add multiple digit numbers by using the column addition method



How to round off a number?

  • Identify the place value of the digit to be rounded - this is called the rounding digit.
  • Identify the next digit to the right of the rounding digit, if there is any:
    • If there is no other digit to the right, then the number is not changing, it stays the same.
    • Rounding down. If there is a digit to the right of the rounding digit and this digit is less than 5 (ie: 0 to 4), then leave the rounding digit as it is and replace all the digits to the right of it with zeros. This is called rounding down.
    • Rounding up. If there is a digit to the right of the rounding digit and this digit is 5 or more (ie: 5 to 9), then increase the rounding digit by 1 and replace all the digits to the right of it with zeros. This is called rounding up.

>> How to round off numbers to whole and decimal places, plus examples