Binary Number System

Computers use binary digits. And some puzzles can be solved using binary numbers.

A Binary Number is made up of only 0s and 1s.

110100
Example of a Binary Number

There is no 2,3,4,5,6,7,8 or 9 in Binary!

How do we Count using Binary?

Binary    
0   We start at 0
1   Then 1
???   But then there is no symbol for 2 ... what do we do?

 

    Decimal    
Well how do we count
in Decimal?
  0   Start at 0
  ...   Count 1,2,3,4,5,6,7,8, and then...
  9   This is the last digit in Decimal
  10   So we start back at 0 again, but add 1 on the left

The same thing is done in binary ...

  Binary    
  0   Start at 0
1   Then 1
•• 10   Now start back at 0 again, but add 1 on the left
••• 11   1 more
•••• ???   But NOW what ... ?

 

    Decimal    
What happens in Decimal ... ?   99   When we run out of digits, we ...
  100   ... start back at 0 again, but add 1 on the left

And that is what we do in binary ...

  Binary    
  0   Start at 0
1   Then 1
•• 10   Start back at 0 again, but add 1 on the left
••• 11    
•••• 100   start back at 0 again, and add one to the number on the left...
... but that number is already at 1 so it also goes back to 0 ...
... and 1 is added to the next position on the left
••••• 101    
•••••• 110    
••••••• 111    
•••••••• 1000   Start back at 0 again (for all 3 digits),
add 1 on the left
••••••••• 1001   And so on!

 

See how it is done in this little demonstration (press play):

Decimal vs Binary

Here are some equivalent values:

Decimal: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Binary: 0 1 10 11 100 101 110 111 1000 1001 1010 1011 1100 1101 1110 1111

Here are some larger equivalent values:

Decimal: 20 25 30 40 50 100 200 500
Binary: 10100 11001 11110 101000 110010 1100100 11001000 111110100

"Binary is as easy as 1, 10, 11."

Now see how you can use Binary to count past 1,000 on your fingers:

Position

In the Decimal System there are the Units, Tens, Hundreds, etc

In Binary, there are Units, Twos, Fours, etc, like this:

This is 1×8 + 1×4 + 0×2 + 1 + 1×(1/2) + 0×(1/4) + 1×(1/8)
= 13.625 in Decimal

Numbers can be placed to the left or right of the point, to indicate values greater than one or less than one.

10.1
The number to the left of the point is a whole number (10 for example)
   
As we move further left, every number place
gets 2 times bigger.
   
The first digit on the right means halves (1/2).
   
  As we move further right, every number place
gets 2 times smaller (half as big).

Example: 10.1

  • The "10" means 2 in decimal,
  • The ".1" means half,
  • So "10.1" in binary is 2.5 in decimal

You can do conversions at Binary to Decimal to Hexadecimal Converter.

Words

The word binary comes from "Bi-" meaning two. We see "bi-" in words such as "bicycle" (two wheels) or "binocular" (two eyes).

When you say a binary number, pronounce each digit (example, the binary number "101" is spoken as "one zero one", or sometimes "one-oh-one"). This way people don't get confused with the decimal number.

A single binary digit (like "0" or "1") is called a "bit". For example 11010 is five bits long.

The word bit is made up from the words "binary digit"

How to Show that a Number is Binary

To show that a number is a binary number, follow it with a little 2 like this: 1012

This way people won't think it is the decimal number "101" (one hundred and one).

Examples

Example: What is 11112 in Decimal?

  • The "1" on the left is in the "2×2×2" position, so that means 1×2×2×2 (=8)
  • The next "1" is in the "2×2" position, so that means 1×2×2 (=4)
  • The next "1" is in the "2" position, so that means 1×2 (=2)
  • The last "1" is in the units position, so that means 1
  • Answer: 1111 = 8+4+2+1 = 15 in Decimal

Example: What is 10012 in Decimal?

  • The "1" on the left is in the "2×2×2" position, so that means 1×2×2×2 (=8)
  • The "0" is in the "2×2" position, so that means 0×2×2 (=0)
  • The next "0" is in the "2" position, so that means 0×2 (=0)
  • The last "1" is in the units position, so that means 1
  • Answer: 1001 = 8+0+0+1 = 9 in Decimal

Example: What is 1.12 in Decimal?

  • The "1" on the left side is in the units position, so that means 1.
  • The 1 on the right side is in the "halves" position, so that means 1×(1/2)
  • So, 1.1 is "1 and 1 half" = 1.5 in Decimal

Example: What is 10.112 in Decimal?

  • The "1" is in the "2" position, so that means 1×2 (=2)
  • The "0" is in the units position, so that means 0
  • The "1" on the right of the point is in the "halves" position, so that means 1×(1/2)
  • The last "1" on the right side is in the "quarters" position, so that means 1×(1/4)
  • So, 10.11 is 2+0+1/2+1/4 = 2.75 in Decimal

"There are 10 kinds of people in the world,
those who understand binary numbers, and those who don't."