212 (decimal) is 11010100 (binary)
-- The decimal system (base-10) uses 10 digits to write all numbers. -- The binary system (base-2) uses 2 digits to write all numbers.
a) 6401 in Binary is 1100100000001b) 1010110 in decimal is 86
There is basically one way to write hexadecimal numbers. Of course, the numbers represent information, and this information can be represented in may other ways; some of them are in binary (4 binary digits for each hexadecimal digit), in decimal, or each byte as as decimal number (as in the dotted decimal notation used for IP version 4 numbers).
It is 127 in decimal numbers.
To convert a decimal number to binary, you divide the decimal number by 2 and write down the remainder. Then, divide the quotient by 2 and write down the remainder again. Repeat this process until the quotient is 0. The binary number is the remainders read in reverse order.
A remainder is the numbers after a decimal point; sometimes used as repesenting in binary to get a binary number from a decimal number.
Write a subscript 2 after the numbers or, as in the question, simply say so.
Decimal 23 is 10111 in binary
Decimal 18 is 10010 in binary
Decimal 26 is 11010 in binary
Decimal 27 is 11011 in binary