Solution

\[ \begin{align*} & \color{magenta}\text{Sum of the first } n \text{ natural numbers } = \frac{n^2 + n}{2} \\ \\ &\text{For the first five natural numbers: } n = 5 \\ \\ \text{Sum } & = \frac{5^2 + 5}{2} \\ \\ & = \frac{25 + 5}{2} \\ \\ & = \frac{30}{2} \\ \\ & = 15 \\ \\ &\text{For the first seven natural numbers: } n = 7 \\ \text{Sum } & = \frac{7^2 + 7}{2} \\ \\ & = \frac{49 + 7}{2} \\ \\ & = \frac{56}{2} \\ \\ & = 28 \\ \\ &\text{Now, for the first ten natural numbers: } n = 10 \\ \text{Sum } & = \frac{10^2 + 10}{2} \\ \\ & = \frac{100 + 10}{2} \\ \\ & = \frac{110}{2} \\ \\ & = 55 \end{align*} \]

Answer \( \color{red} 55 \)