To denote the base, we use a subscript or a prefix. Thus, 1011₂ means the same thing as 0b1011.

1011₂ = 11₁₀
0b1011 = 11
0x0B = 11
0o13 = 11

Hexadecimal and octal are compact notations for binary numbers: Each hexadecimal digit corresponds to exactly 4 bits, and each octal digit corresponds to exactly 3 bits.