Let’s Understand About 2 ‘s Complement Subtraction

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Want to know more about 2’s complement subtraction for kids? Well, you’ve come to the right place! This article discusses 2’s addition and how it works with additions by subtraction. Two binary numbers can be subtracted using the second’s complement approach. By the end of this article, you should be more confident in performing 2’s complement subtraction, including binary subtraction using 2’s addition. Let’s start!

What is 2’s complement?

To implement this method of subtracting two binary numbers, the first step is to find the 2’s complement of the number subtracted from the other number. To get 2’s complement, first find 1’s complement and then add 1. Addition requires 2’s addition.

Suppose we need to find the 2’s complement of the binary number 10010. First let’s find the 1’s complement. To find this, change all 1’s to 0’s and all 0’s to 1’s. Therefore, 1’s complement 10010 will be 01101. Add 1 to this and we will get 2’s complement, i.e. 01110.

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Binary subtraction using 2’s complement

To learn how to subtract binary numbers using 2’s addition, which is subtracting a smaller number from a larger number using 2’s complement subtraction, follow these steps:

  • Step 1: Determine the 2’s complement of a small number

  • Step 2: Add this to the larger number.

  • Step 3: Skip the ride. Note that in this case there is always a carry.

The following example illustrates the above steps:

Example: subtract $(1010)_2$ from $(1111)_2$ using the 2’s complement method.

Answer:

This is shown below:

Subtraction using the 2’s complement method

To subtract a larger number from a smaller number using 2’s complement subtraction, the following steps must be performed:

  • Step 1: Determine the 2’s complement of a small number.

  • Step 2: Add this to the larger number.

  • Step 3: In this case there is no bearing. The result is in 2’s complement form and is negative.

  • Step 4: To get the answer in true form, take 2’s complement and change its sign.

Example: Subtract $(1010)_2$ from $(1000)_2$ using 2’s complement.

Answer:

2's complement

2’s complement

Step 3 and Step 4 are described in Calculating Differences above.

Subtraction using r’s complement:

Let’s say you want to subtract the number 01010100 from 11100011. We can do this using 2’s complement, just subtracting using r’s complement.

Steps to find the complement of r:

To find the complement of r, add 1 to the computed ($r-1$) complement.

Here’s an example:

P. Find the complement of 7 and 8 of the number $(5 63)_8$

  • Step 1: Identify the base (or) radix. Here $r=8$.

  • Step 2: Since 7 is the largest digit in the number system, subtract each digit of the given number from 7, ie if it is a three-digit number, subtract the number from 777.

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$therefore(214)_8$ is the complement of the given number 7

  • Step 3: Find r’s complement i.e. 8’s complement, then add ‘1’ to the result of 7’s complement number.

$therefore(215)_8$ is the addition of 8 of the given number.

Solved examples

Q 1. 10110 – 11010

Answer: 11010 has 2s complement (00101+1) or 00110.

Add 2’s complement to the minuend (10110+00110) or 11100.

Now I get his complement;

The solution is (00011+1)= – (00100)

Q 2. 10110-01111

Answer: 2s complement of 01111 is 10001.

Minuend plus two’s complement (10110-10001) equals 100111.

The answer is 00111.

Q 3. 0100-11101

Answer: 2s complement of 11101 is 00011

Minuend plus two’s complement (10100-00011) equals 10111.

Since there is no bearing here, the answer is 01001.

Q 4. 110101 – 101001

Answer: The complement of 101001 in 2 is 010111

(110101-010111) Add the minuend and 2’s complement to get 1001100.

carry, the leftmost bit of the result is 1 and is ignored.

The answer is 001100.

Exercise questions

Q 1. 1001 – 0100

Answer: 0101

Q 2. 0100 – 1011 AD

Answer: 1011

Q 3. 0110 – 0100

Answer: 0010

Q 4. 10110-11101

Answer: 00111

Q5. 110-101

Answer: 001

Summary

In conclusion, in this article we looked at subtracting two’s complement. We’ve made an example problem to show you how it works and how it’s done on paper. The examples in this article are for demonstration purposes only and therefore do not necessarily represent the types of problems you will encounter on a standardized test.

Instead of just memorizing the steps in this article, you should practice the problems. You can use paper and pencil or use a calculator, a 2’s addition subtraction calculator or your fingers on your smartphone. Therefore, if you want to perform division (and thus subtraction) without using r’s complement, you must learn how to use 2’s complement when performing division.

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