In the binary number system which is used in computer operations, there are only two digits allowed: 0 and 1. How many different binary numbers can be formed using at most four binary digits?

1 Answer
May 15, 2018

#30#

Explanation:

The total number is the sum of all possible numbers with one, two, three or four digits.

There are exactly #2^n# numbers with #n# digits: for each digit you have two choices (it can be either #0# or #1#). So, you have

  • #2^1 = 2# numbers with one digit (#0# and #1#)
  • #2^2 = 4# numbers with two digits (#00#, #01#, #10#, #11#)
  • #2^3 = 8# numbers with three digits (#000#, #001#, #010#, #011#, #100#, #101#, #110#, #111#)
  • #2^4 = 16# numbers with three digits (#0000#, #0001#, #0010#, #0011#, #0100#, #0101#, #0110#, #0111#, #1000#, #1001#, #1010#, #1011#, #1100#, #1101#, #1110#, #1111#)

So, you have #2+4+8+16 = 30# numbers with at most four digits.