1. **Stating the problem:** Majed starts with 2 magic stones. Each time the stones are rubbed once, each stone produces one new stone, effectively doubling the total number of stones. 2. **Understanding the process:** After rubbing once, the number of stones doubles. After rubbing twice, the number doubles again, and so on. 3. **Formula used:** The number of stones after $n$ rubs is given by: $$\text{Number of stones} = 2 \times 2^n = 2^{n+1}$$ where $n$ is the number of times the stones are rubbed. 4. **Goal:** Find $n$ such that the number of stones equals $k$ (the desired number of stones): $$k = 2^{n+1}$$ 5. **Solving for $n$:** Take the logarithm base 2 of both sides: $$\log_2(k) = n + 1$$ $$n = \log_2(k) - 1$$ 6. **Interpretation:** The stones must be rubbed $n = \log_2(k) - 1$ times to get $k$ stones. 7. **Important note:** This formula only works if $k$ is a power of 2 and $k \geq 2$ because the number of stones doubles each time starting from 2. **Final answer:** $$n = \log_2(k) - 1$$