Binary numbers are a base-2 system as there are only 2 digits, 0 and 1.

The binary number 11011 is:

2^4  2^3  2^2  2^1  2^0 (what each column is worth in scientific)

 16     8     4      2     1    (what each column is worth in decimal)

  1      1     0      1     1

In other words, one 16, one 8, no 4, one 2 and a 1:

16 + 8 + 0 + 2 + 1 = 27

Repeated Division Method:

1. Divide the given decimal number by 2 and note down the remainder.
2. Now, divide the obtained quotient by 2, and note the remainder again.
3. Repeat the above steps until you get 0 as the quotient.
4. Now, write the remainders in reverse order so that the last remainder is written first, and the first written last.

Example Question:

Convert the decimal number 242 to binary

Remember: The first remainder will be the Least Significant Bit (LSB) while the last remainder is the Most Significant Bit (MSB).

Method:

Add up the decimal column values for each column with a 1 in it. 

(You may find it useful to write the values above the binary number first)

Example Question:

Convert the binary number 10011101 to decimal

1 x 128 + 0 x 64 + 0 x 32 + 1 x 16 + 1 x 8 + 1 x 4 + 0 x 2 + 1 x 1

= 128 + 16 + 8 + 4 + 1 

= 157