Question

Sol. [Key Concept: Arithmetic growth — Lₜ = L₀ + rt]

Arithmetic growth can be expressed as:

$$\begin{matrix} & L_{t} = L_{0} + rt\ \ \left\lbrack \text{~}\text{where,}\text{~}L_{t} = \text{~}\text{length at time '}\text{~}t\text{~}\text{',}\text{~}L_{0} = \text{~}\text{Length at time 'zero',}\text{~}r = \text{~}\text{growth rate}\text{~} \right.\ \text{~}\text{]}\text{~} \\ & \begin{matrix} L_{7\text{~}\text{th day}\text{~}} \Rightarrow 20 + 30 \times 7 \\ \ \ \ \ \ \ \ \ \ \ \ \Rightarrow 20 + 210 \\ \ \ \ \ \ \ \ \ \Rightarrow 230\text{ }cm \end{matrix} \end{matrix}$$

The length of the stem at the end of $7^{\text{th}\text{~}}$ day is 230 cm.