Explanation

To convert the decimal number 139 to binary:

139 ÷ 2 = 69 remainder 1

69 ÷ 2 = 34 remainder 1

34 ÷ 2 = 17 remainder 0

17 ÷ 2 = 8 remainder 1

8 ÷ 2 = 4 remainder 0

4 ÷ 2 = 2 remainder 0

2 ÷ 2 = 1 remainder 0

1 ÷ 2 = 0 remainder 1

Reading the remainders from bottom to top:

10001011