How to Subtract

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Subtraction is a simple mathematical operation that determines the difference between two numbers. Subtract smaller numbers mentally or use a pen and paper or electronic device for more complicated subtractions. Subtracting is a part of many math classes and courses, in addition to many household and business activities involving money, time or anything with numbers. Learn how to subtract with a few simple steps, some careful attention and a bit of practice.

Things You'll Need

  • Writing implement
  • Piece of paper
  • Write the first number on a sheet of paper. Write the number to be subtracted underneath the first number. Write a dash, (representing a minus sign) next to the lower number to indicate that the operation is one of subtraction. Count the difference between the two and the result is the answer. Write the answer as the third number in this column, separated by a line to show that it is the result of the operation above.

  • Place double digits in columns before beginning. Start on the right with the simple subtraction described in step one. If the number below is larger than the number above, a digit (in the majority of cases a 1) must be borrowed from the column to the left. For example, in the equation 26 - 7, begin by subtracting 7 from 16. Notice that the number 1 in 16 has been borrowed from the 2 in 26. Remember that the 2 in 26 is now one less. 16-7 is 9. The 2 in 26 has now become a 1. Since there is no second digit in 7 to be subtracted from 26, carry down the 1 and place it next to the 9. The result of 26 - 7 is 19.

  • Check your work by adding the answer and the number being subtracted (the lower of the first two) together. Your answer is correct if the result of your adding results in the first number of the subtraction equation. Here is an example of a subtraction equation followed by a checking equation: 5 - 3 = 2 and then 2 + 3 = 5.

Tips & Warnings

  • Attention to detail and keeping track of borrowed numbers is very important for accuracy when subtracting. If the number you are subtracting from the original number has a decimal point with more numbers to the right of it than the original number, simply add a decimal and an equal number of 0's to the original number so that borrowing becomes clearer. For example 20 - 15.546 is easier to subtract when written as 20.000 - 15.546.
  • Subtracting a negative number from another number is a more advanced mathematical situation. In this case the operation turns into addition. 10 minus negative 4, otherwise written 10 - (-4), actually results in 10 + 4, which is 14. Taking negative 4 away from 10 is the same as adding 4 to 10.

References

  • Photo Credit Creatas/Creatas/Getty Images
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