Answer to Question #87224 in Abstract Algebra for malti

Question

a) If G is a group of order 40, and H and K are its subgroups of orders 20 and 10,
then check whether or not HK ≤ G . Further, show that o(H∩K) ≥ 5.
b) Prove that C*/S~=R+, where S ={z∈C*| |z|=1}, R+ ={x∈R| x>0} and C*=C\{0}.
c) What are the possible algebraic structures of a group of order 99?