Regular expression for language which consist of exactly two b’s over the set ∑={a,b} =>  a*ba*ba*

Regular expression for all binary string with at least 3 characters and 3rd character should be zero =>  (0+1)(0+1)0(0+1)*

Regular expression for string start with 1 and end with 0 =>  1(0+1)*0

Regular expression for string end with abb =>(a+b)*abb

Regular expression for string of 0 and 1 end with 00 => (0+1)*00

Regular expression for String starts and ends with same character 0(0+1)*0     or 1(0+1)*1 or a(a+b)*a or b(a+b)*b

Regular expression for binary number starts and end with 1. => 1(0+1)*1

Regular expression for binary number end with 1 =>  (0+1)*1

Regular expression for binary number end with 0 =>   (0+1)*0

Regular expression for 1 or more occurrence of either a or b or both =>     (a+b)+