Brainlag PlusTwo's complement, where the left bit is worth a negative number, and subtraction by adding. Needed for Edexcel 1CP2 and for A-level.
Two's complement
In two's complement, the left bit is worth a negative amount.
In 8 bits it is worth −128; the others are worth +64 down to +1 as usual.
- 1111 0110 = −128 + 64 + 32 + 16 + 4 + 2 = −10.
- A negative number always starts with 1; a positive one with 0.
- 8 bits store −128 to +127. In general, n bits store −2^(n − 1) to 2^(n − 1) − 1.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 4, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards