According to the question the metre scale having a weight of $50\text{ gf}$ is balanced at 40 $\text{ cm}$ mark without any weight suspended on it. So, its weight acts at $40\text{ cm}$ mark which is also the centre of gravity of this non-uniform metre scale. Thus, $0\text{ cm}$ to $40\text{ cm}$ length will have a weight of $25\text{ gf}$ And, $40\text{ cm}$ to $100\text{ cm}$ length will have a weight of $25\text{ gf}$. Thus, if we cut this ruler from $50\text{ cm}$ mark (i.e. centre), the part 0 to $50\text{ cm}$ part of the ruler will weigh more than $25\text{ gf}$.