What is the effective spring constant formula used to calculate the overall stiffness of a system with multiple springs connected in parallel or in series?

The effective spring constant formula for springs connected in parallel is: 1/keff 1/k1 1/k2 1/k3 ... where keff is the overall stiffness and k1, k2, k3, etc. are the individual spring constants. For springs connected in series, the formula is: keff k1 k2 k3 ...