Two closely coiled helical springs with stiffness k₁ and k₂ respectively are connected in series. The stiffness of an equivalent spring is given by

A. $$\frac{{{{\text{k}}_1}{{\text{k}}_2}}}{{{{\text{k}}_1} + {{\text{k}}_2}}}$$

B. $$\frac{{{{\text{k}}_1} - {{\text{k}}_2}}}{{{{\text{k}}_1} + {{\text{k}}_2}}}$$

C. $$\frac{{{{\text{k}}_1} + {{\text{k}}_2}}}{{{{\text{k}}_1}{{\text{k}}_2}}}$$

D. $$\frac{{{{\text{k}}_1} - {{\text{k}}_2}}}{{{{\text{k}}_1}{{\text{k}}_2}}}$$

Answer: Option A