Hi! I haven't done anything with the following problem because I really don't know where to start from. My book doesn't give any guideline. The only thing I am aware of is F=-Kx and E=Kx^2/2 but I cannot use them to proceed in some way. '' A spring of length l it is consisted of 2 springs. The first has constant k and length l/2 and the second has constant 2k and length l/2. Prove that the constant of the hole spring is 2k/3.'' I am sorry for the bad english. My mother tongue is greek. Thank you.